• Aucun résultat trouvé

Matrix Product State Simulations of Non-equilibrium Steady States and Transient Heat Flows in the Two-Bath Spin-Boson Model at Finite Temperatures

N/A
N/A
Protected

Academic year: 2021

Partager "Matrix Product State Simulations of Non-equilibrium Steady States and Transient Heat Flows in the Two-Bath Spin-Boson Model at Finite Temperatures"

Copied!
25
0
0

Texte intégral

(1)

HAL Id: hal-03083803

https://hal.sorbonne-universite.fr/hal-03083803

Preprint submitted on 19 Dec 2020

HAL is a multi-disciplinary open access

archive for the deposit and dissemination of

sci-entific research documents, whether they are

pub-lished or not. The documents may come from

teaching and research institutions in France or

abroad, or from public or private research centers.

L’archive ouverte pluridisciplinaire HAL, est

destinée au dépôt et à la diffusion de documents

scientifiques de niveau recherche, publiés ou non,

émanant des établissements d’enseignement et de

recherche français ou étrangers, des laboratoires

publics ou privés.

Matrix Product State Simulations of Non-equilibrium

Steady States and Transient Heat Flows in the

Two-Bath Spin-Boson Model at Finite Temperatures

Angus Dunnett, Alex Chin

To cite this version:

(2)

Matrix Product State Simulations of Non-equilibrium

Steady States and Transient Heat Flows in the

Two-Bath Spin-Boson Model at Finite Temperatures

Angus J Dunnett

1

and Alex W Chin

1,

1

Insitut des Nanosciences de Paris, Sorbonne Universit, CNRS, Place Jussieu,Paris, 75005

*

Correspondence: [email protected]

Version December 19, 2020 submitted to Journal Not Specified

Abstract:

Simulating the non-perturbative and non-Markovian dynamics of open quantum systems

1

is a very challenging many body problem, due to the need to evolve both the system and

2

its environments on an equal footing. Tensor network and matrix product states (MPS) have

3

emerged as powerful tools for open system models, but the numerical resources required to treat

4

finite-temperature environments grow extremely rapidly and limit their applications. In this study

5

we use time-dependent variational evolution of MPS to expore the striking theory of Tamescelli et

6

al. [

1

] that shows how finite-temperature open dyanmics can be obtained from zero temperature,

7

i.e. pure wave function, simulations. Using this approach, we produce a benchmark data set for the

8

dynamics of the Ohmic spin-boson model across a wide range of coupling and temperatures, and

9

also present detailed analysis of the numerical costs of simulating non-equilibrium steady states, such

10

as those emerging from the non-perturbative coupling of a qubit to baths at different temperatures.

11

Despite ever growing resource requirements, we find that converged non-perturbative results can be

12

obtained, and we discuss a number of recent ideas and numerical techniques that should allow wide

13

application of MPS to complex open quantum systems.

14

Keywords:

Open quantum systems, Tensor networks, non-equilibrium dynamics

15

1. Introduction

16

The physics of open quantum systems (OQS) plays a critical role in almost all aspects of quantum

17

science [

2

,

3

], and the emergent phenomena of dephasing, decoherence and dissipation particularly

18

limit our ability to initialise and control multi-partite quantum states. As a direct result of this, the

19

development of scalable quantum technologies is greatly constrained by open system phenomena,

20

and understanding how irreversibility arises from microscopic system-environment interactions has

21

become essential for finding ways to mitigate deleterious noise effects [

4

]. However, alongside this

22

goal of suppressing dissipative noise - normally by making the systems less ‘open’ - the theory of

23

OQS also plays a vital role in the design of systems where the exploitation of strong energy and

24

information exchange between a system and its environment is desirable: this is the world of quantum

25

thermodynamics and nanoscale energy harvesting, storage and transduction [

5

7

].

26

Any ‘machine’ or device capable of converting ambient energy into work must necessarily be

27

an open system. As these machines shrink to lengths where such energetic transformations can

28

become few-quanta, ultra-fast events, it becomes necessary to describe their functional dynamics on

29

timescales over which system-environment correlations - in both space and time - may be highly

30

relevant [

8

,

9

]. Unlike the perturbative OQS found, for example, in atomic systems where dissipation

31

can be characterised by simple decay rates, quantum energy harvesting naturally focuses on the

32

highly non-Markovian and non-perturbative regime of OQS where the border between the ‘system’

33

(3)

and ‘environment’ degrees of freedom is ill-defined. Moreover, as systems capable of converting

34

thermal energy must also reject a certain amount of heat to a colder reservoir [

7

], the study of quantum

35

energy harvesting leads directly to a consideration of multi-environment OQS, and the extended,

36

inter-environmental quantum correlations that could be generated under non-equilibrium operating

37

conditions.

38

Molecular and biological light-harvesting systems provide a good example of such nanoscale

39

energy extraction, in which a non-thermal population of electronic excitations (excitons, charge

40

pairs...) appears from the molecule-mediated connection of the ‘hot’ photon and ‘cold’ vibrational

41

environments. In this context, much attention has been placed on the complex physics due to the

42

strong coupling and non-separable timescales of electronic and environmental (vibrational) dynamics

43

[

10

12

], which include potentially exploitable effects such as transient breaking of detailed balance

44

[

13

], noise-induced electronic coherence and cooperative multi-environment effects [

14

,

15

]. In such

45

studies, the effect of light is normally assumed to be weak, leading to the ‘additive’ approximation

46

that phenomenological terms describing excitation, emission and dephasing can be simply added to

47

the more complex equations of motion of the vibronic open system. However, organic molecules often

48

have very strong light-matter coupling and can show surprising non-additive effects [

16

,

17

], including

49

nonlinear polaritonic weakening of exciton-phonon coupling in micro-cavity systems [

18

].

50

The example above highlights the theoretical challenges posed by some energy harvesting

51

systems: non-perturbative and highly structured couplings, comparable dynamical timescales and

52

competing environmental processes. Under these conditions the dissipative dynamics of the system’s

53

reduced density matrix cannot be simply described by dephasing and relaxation rates: the full

54

real-time evolution of the system and its environments must be accounted for on an essentially equal

55

footing. This looks, a priori, like a hopeless task, as each environment contains a continuum of

56

quantum excitation modes, and the formal number of quantum states in any computation will explode

57

exponentially with the number of such modes. However, things are not so desperate, and two broad

58

responses to this problem have emerged over recent years: one branch aims to efficiently simulate

59

the propagators of the system’s reduced density matrix [

10

,

19

21

], the other aims at representing

60

and evolving the entire system-environment wave function. Important contributions in this latter

61

domain are Density Matrix Renormalization Group (DMRG) techniques such as the Time Evolving

62

Density with Orthogonal Polynomials Approach (TEDOPA) [

22

,

23

], Dissipation-Assisted Matrix

63

Product Factorization [

24

], Time-Dependent Numerical Renormalisation Group techniques and the

64

Multi-Layer Multi Configurational Time-Dependent Hartree method (ML-MCTDH) developed in

65

Chemical physics [

25

,

26

].

66

The key to all of the wave function methods is the observation that, given a well-defined

67

initial condition, the quantum dynamics generated by typical system-environment Hamiltonians

68

leave the state inside a much smaller sub-space of the complete Hilbert space of the problem. This

69

suggests that the wave function can be parameterised by a potentially tractable number of parameters,

70

and - as we shall see - the effectively short-range, one-dimensional structure of OQS Hamiltonians

71

implies that Matrix Product States (MPS) will provide an efficient and versatile format for many

72

system-environment wave functions. Viewed this way, the parameters (matrices) of an MPS can be

73

considered as variational degrees of freedom, leading to the powerful 1-site time-dependent variational

74

principle (1TDVP) algorithm for efficient propagation of large wave functions in real-time [

27

]. This

75

general technique can be used in any MPS and Tree-Tensor Network problem [

15

], but it’s particular

76

utility in open-system problems has only recently been appreciated. We shall make use of this technique

77

in this article, but a discussion of MPS, TDVP and other computational aspects is left to the dedicated

78

presentations in the literature [

27

30

].

79

Instead, the key issue that we wish to explore in this study is the remarkable recent result of

80

Tamascelli et al. [

1

] that allows wave function approaches to OQS to effectively capture the effects of

81

finite temperature environments through the simulation of an equivalent zero-temperature proxy system.

82

As already discussed above, in the non-perturbative, non-Markovian regime of OQS, computing the

(4)

evolution of the single wave function from a sharp initial condition can already be very demanding:

84

converging results over the astronomically large space of initial conditions in a thermal ensemble

85

rapidly becomes impossible. If we also wish to explore the role of non-classical effects in heat flows

86

between finite-temperature environments, the problem becomes exponentially worse. The access to

87

finite temperature properties from a single zero-temperature (pure) wave function simulation thus

88

opens up an entire class of powerful non-perturbative methods for the study of novel open quantum

89

systems. This work aims to establish the extent to which Tamascelli’s ‘T-TEDOPA’ theory translates

90

into affordable non-perturbative TDVP simulations of thermal and non-equilibrium OQS dynamics, as

91

well as to explore some of the non-classical and non-additive aspects of heat exchange in OQS.

92

This article is organised as follows. In Section

2.1

we present the spin-boson Hamiltonians that

93

we will simulate. Sections

2.2

&

2.3

give a summary of the T-TEDOPA theory that we will employ

94

in our numerical investigations. Section

2.4

then presents a careful study of the non-perturbative

95

spin-boson model at finite temperatures which reveals some of the practical numerical costs implicit in

96

this approach. Thanks to this testing, we are able to offer a freely accessible data set that can be used

97

as a benchmark for other numerical approaches to this model, as well as code packages that allow

98

users to perform their own TDVP calculations on finite-temperature open systems. In anticipation

99

of the need to explore non-equilibrium states in a wide range of future contexts, we go on to test

100

the non-perturbative physics of a two-level system (TLS) coupled to two environments at different

101

temperatures in Section

2.5

. Exploiting the information in the many-body system-environment(s)

102

wave function, we examine the microscopic behaviour of the heat flows between the system and the

103

environments as a function of environmental coupling strength and temperature differences, and

104

highlight a number of non-additive effects arising from non-perturbative quantum polaron effects.

105

Finally, we summarise and discuss our findings in Section

3

.

106

2. Results

107

2.1. Model, parameters and initial conditions

108

We shall base our exploration of finite temperature open dynamics on numerical simulations and

109

analysis of a quantum two-level system that is strongly coupled to either one or two baths of bosonic

110

harmonic oscillators, as illustrated in Figure

1

a. The two baths are labelled a and b and are at different

111

inverse temperatures β

a

and β

b

, respectively (β

=

1/

(

k

b

T

)

). The system-bath Hamiltonian is given by

112

ˆ

H

=

ω

0

2

σz

+

H

ˆ

a

I

+

H

ˆ

b

I

+

H

ˆ

a

B

+

H

ˆ

B

b

,

(1)

where

ˆ

H

a

I

=

σ

x

k

(

g

k

ˆa

k

+

g

k

ˆa

k

)

(2)

ˆ

H

b

I

=

σx

k

(

g

k

ˆb

k

+

g

k

ˆb

k

)

(3)

ˆ

H

B

a

=

k

ω

k

ˆa

k

ˆa

k

(4)

ˆ

H

B

b

=

k

ω

k

ˆb

k

ˆb

k

.

(5)

The TLS is described by the standard Pauli operators σ, while the ˆa

k

(

ˆb

k

)

are bosonic anihilation

113

operators for harmonic modes of frequency ω

k

in bath a

(

b

)

. The corresponding creation operators are

114

denoted ˆa

k

(

ˆb

k

)

. The k harmonic of each bath couples to the TLS with a coupling strngth denoted g

k

,

115

which we take to depend on the index k but not on a or b.

116

The spectral density of the environment is defined as J

(

ω

)

π

k

|

g

k

|

2

δ

(

ω

ω

k

)

, where δ

(

x

)

is

(5)

take various forms in specific physical realisations such as electron-phonon interactions, emitter-photon

or exciton-vibration coupling in molecular systems. It is well known that the qualitative behaviour of

the TLS depends sensitively on the form of J

(

ω

)

, especially at low temperatures [

19

]. For simplicity, we

assume identical system-bath couplings for both environments and use the common linear frequency

dependence that defines an Ohmic environment ω

c

J

(

ω

) =

2παωθ

(

ωc

ω

)

,

(6)

where α is a dimensionless coupling constant and we have introduced a hard frequency cut-off ω

c

.

117

The initial condition ˆρ

(

0

)

for our numerical simulations is taken to be an uncorrelated (product)

state of the spin and baths, which - because of the baths’ finite temperatures - must be described by a

mixed state, i.e. a density matrix

ˆρ

(

0

) =

ρs

e

− ˆ

H

a

B

β

a

Tr

{

e

− ˆ

H

a

B

β

a

}

e

− ˆ

H

b

B

β

b

Tr

{

e

− ˆ

H

b

B

β

b

}

,

(7)

where ρ

s

is some arbitrary initial density matrix for the TLS.

118

Remarkably, despite the initial condition containing two statistically mixed thermal density

119

matrices, it has recently been shown by Tamascelli et al. that the reduced dynamics of the spin can still

120

be obtained from a single simulation of an equivalent pure , i.e. zero temperature, system-environment

121

wave function [

1

,

31

]. As this result is central for generating our numerical results and our later

122

discussion, we shall now give a brief summary of the protocol first presented in Ref. [

1

].

123

2.2. Finite-temperature reduced dynamics from pure wave function evolution

124

In this section we shall closely follow the original notation and presentation of Tamascelli et al [

1

]

and, to simplify the presentation, we shall only consider the coupling to a single environment denoted

E. The procedure can be easily generalised to multiple environments. Our starting point is the generic

Hamiltonian for a system coupled to a bosonic environment consisting of a continuum of harmonic

oscillators

H

SE

=

H

S

+

H

E

+

H

I

,

(8)

where

H

I

=

A

S

Z

0

dω ˆ

O

ω

, H

E

=

Z

0

dωωa

ω

a

ω

.

(9)

The Hamiltonian H

S

is the free system Hamiltonian and A

S

is a generic system operator which couples

to the bath. The Environment’s free Hamiltonian is given by H

E

. For the bosonic bath operators we

take the displacements

O

ω

=

q

J

(

ω

)(

a

ω

+

a

ω

)

,

(10)

thus defining the spectral density J

(

ω

)

. This has been written here as an arbitrary continuous function,

125

but we note that the formulas can also be applied to the case of coupling to a discrete set of vibrational

126

modes by adding suitable structure to the spectral density, i.e. sets of lorentzian peaks or Dirac

127

functions [

32

34

].

128

The state of the system+environment at time t is a mixed state described by a density matrix

129

ρ

SE

(

t

)

. The initial condition is assumed to be a product of system and environment states ρ

SE

(

0

) =

130

ρS

(

0

)

ρE

(

0

)

where ρ

S

(

0

)

is an arbitrary density matrix for the system and ρ

E

(

0

) =

exp

(

H

)

/

Z

,

131

with the environment partition function given by

Z =

Tr

{

exp

(

H

E

β

)

}

. Such a product state is

132

commonly realised in non-equilibrium problems where the system is suddenly prepared or projected

133

into an excited state from a ground state in which the system and environment states are separable.

134

This type of preparation is exemplified by the Franck-Condon principle in molecular photophysics,

135

where the optical transition occurs without any change in the nuclear degrees of freedom, leaving the

136

subsequent relaxation dynamics to evolve from a product ’initial’ condition [

35

,

36

]. The environment

(6)

thus begins in a thermal equilibrium state with inverse temperature β, and the energy levels of each

138

harmonic mode are statistically populated. For a very large number (continuum) of modes, the number

139

of possible thermal configurations grows extremely rapidly with temperature, essentially making

140

it impossible to obtain a converged sampling of these configurations when each instance involves

141

demanding wave function simulations. We briefly note that some more efficient sampling methods

142

involving sparse grids and/or stochastic mean-field approaches have recently been proposed and

143

demonstrated [

37

,

38

], as well as some effective MPS techniques for capturing finite temperature effects

144

in frequency domain simulations [

39

].

145

The initial thermal condition of the environmental oscillators is also a Gaussian state, for which it

is further known that the influence functional [

2

] - which is a full description of the influence of the

bath on the system - will depend only on the two-time correlation function of the bath operators

S

(

t

) =

Z

0

h

O

ω

(

t

)

O

ω

(

0

)

i

.

(11)

Any two environments with the same S

(

t

)

will have the same influence functional and thus give rise

146

to the same reduced system dynamics, i.e. the same ρ

S

(

t

) =

Tr

{

ρ

SE

(

t

)

}

. That the reduced density

147

matrix’s dynamics are completely specified by the spectral density and temperature of a Gaussian

148

environment has been known for a long time [

2

], but the key idea of the equivalence - and thus the

149

possibly of the interchange - of environments with the same correlation functions has only recently

150

been demonstrated by Tamascelli et al. [

31

].

151

The time dependence in eq.

11

refers to the interaction picture so that the bath operators evolve

under the free bath Hamiltonian: O

ω

(

t

) =

e

iH

E

t

O

ω

(

0

)

e

−iH

E

t

. Using eq.

10

and

h

a

ω

a

ω

i =

n

β

(

ω

)

we

have

S

(

t

) =

Z

0

J

(

ω

)[

e

−iωt

(

1

+

n

β

(

ω

)) +

e

iωt

n

β

(

ω

)]

.

(12)

Making use of the relation

1

2

(

1

+

coth

(

ωβ

/2

))

(

n

ω

(

β

)

, ω

0

−(

n

|ω|

(

β

) +

1

)

, ω

<

0

(13)

we can write eq.

12

as an integral over all positive and negative ω

S

(

t

) =

Z

−∞

dωSign

(

ω

)

J

(

|

ω

|)

2

(

1

+

coth

(

ωβ

2

))

e

−iωt

.

(14)

But eq.

14

is exactly the two-time correlation function one would get if the system was coupled to a

bath, now containing positive and negative frequencies, at zero temperature! The effects of the finite,

physical temperature now appear in a new effective spectral density for the extended environment

given by

J

β

(

ω

) =

Sign

(

ω

)

J

(|

ω

|)

2

(

1

+

coth

(

ωβ

2

))

.

(15)

Thus, we find that our open system problem is completely equivalent to the one governed by the

Hamiltonian

H

=

H

S

+

H

ext

E

+

H

ext

I

,

(16)

(7)

and which has the initial condition ρ

SE

(

0

) =

ρS

(

0

)

⊗ |

0

i

E

h

0

|

. This transformed initial condition is now

152

far more amenable to simulation as the environment is now described by a pure, single-configuration

153

wave function, rather than a statistical mixed state, and so no statistical sampling is required to capture

154

the effects of temperature on the reduced dynamics!

155

Analysing the effective spectral density of Eq.

15

, it can be seen that the new extended environment

156

has thermal detailed balance between absorption and emission processes encoded in the ratio of the

157

coupling strengths to the positive and negative modes in the extended Hamiltonian (see Figure

1

c), as

158

opposed to the operator statistics of a thermally occupied state of the original, physical mode, i.e.

159

J

β

(

ω

)

J

β

(

ω

)

=

h

a

ω

a

ω

i

β

h

a

ω

a

ω

i

β

=

e

βω

(18)

Indeed, from the system’s point of view, there is no difference between the absorption of a

160

quantum from a thermally occupied, positive energy bath mode and the creation (emission) of an

161

excitation into an unoccupied, negative energy, bath mode. The extension to negative frequencies

162

essentially allows the process whereby the system would be heated by the environment (absorbing

163

pre-existing quanta in the thermal bath) to be mimicked by spontaneous emission into a negative

164

energy vacuum of states, as shown in Figure

1

b.

165

In fact, the equivalence between these two environments goes beyond the reduced system

166

dynamics as there exists a unitary transformation which links the extended environment to the original

167

thermal environment. This means that one is able to reverse the transformation and calculate thermal

168

expectations for the actual bosonic bath such as

h

a

ω

(

t

)

a

ω

(

t

)

i

β

. This is particularly useful for molecular

169

systems in which environmental (vibrational) dynamics are also important observables that report on

170

the mechanisms and pathways of physio-chemical transformations [

40

42

]. In this article, we will use

171

this capability later to look at the non-equilibrium heat flows between the TLS and its environments.

172

This is a major advantage of many-body wave function approaches, as full information about the

173

environment is available, cf. effective master equation descriptions which are obtained after averaging

174

over the environmental state.

(8)

T=0K

T=0K

+E

-E

0

a

<latexit sha1_base64="L7GVLX3zEiot9JRyFWQb1DEVmVI=">AAAB7nicbVDLSgNBEJz1GeMr6tHLYBA8hV0R9Bj04jGCeUCyhN5JbzJk9sFMrxCWfIQXD4p49Xu8+TdOkj1oYkFDUdVNd1eQKmnIdb+dtfWNza3t0k55d2//4LBydNwySaYFNkWiEt0JwKCSMTZJksJOqhGiQGE7GN/N/PYTaiOT+JEmKfoRDGMZSgFkpXYvQII+9CtVt+bOwVeJV5AqK9DoV756g0RkEcYkFBjT9dyU/Bw0SaFwWu5lBlMQYxhi19IYIjR+Pj93ys+tMuBhom3FxOfq74kcImMmUWA7I6CRWfZm4n9eN6Pwxs9lnGaEsVgsCjPFKeGz3/lAahSkJpaA0NLeysUINAiyCZVtCN7yy6ukdVnz3Jr3cFWt3xZxlNgpO2MXzGPXrM7uWYM1mWBj9sxe2ZuTOi/Ou/OxaF1zipkT9gfO5w81HY94</latexit><latexit sha1_base64="L7GVLX3zEiot9JRyFWQb1DEVmVI=">AAAB7nicbVDLSgNBEJz1GeMr6tHLYBA8hV0R9Bj04jGCeUCyhN5JbzJk9sFMrxCWfIQXD4p49Xu8+TdOkj1oYkFDUdVNd1eQKmnIdb+dtfWNza3t0k55d2//4LBydNwySaYFNkWiEt0JwKCSMTZJksJOqhGiQGE7GN/N/PYTaiOT+JEmKfoRDGMZSgFkpXYvQII+9CtVt+bOwVeJV5AqK9DoV756g0RkEcYkFBjT9dyU/Bw0SaFwWu5lBlMQYxhi19IYIjR+Pj93ys+tMuBhom3FxOfq74kcImMmUWA7I6CRWfZm4n9eN6Pwxs9lnGaEsVgsCjPFKeGz3/lAahSkJpaA0NLeysUINAiyCZVtCN7yy6ukdVnz3Jr3cFWt3xZxlNgpO2MXzGPXrM7uWYM1mWBj9sxe2ZuTOi/Ou/OxaF1zipkT9gfO5w81HY94</latexit><latexit sha1_base64="L7GVLX3zEiot9JRyFWQb1DEVmVI=">AAAB7nicbVDLSgNBEJz1GeMr6tHLYBA8hV0R9Bj04jGCeUCyhN5JbzJk9sFMrxCWfIQXD4p49Xu8+TdOkj1oYkFDUdVNd1eQKmnIdb+dtfWNza3t0k55d2//4LBydNwySaYFNkWiEt0JwKCSMTZJksJOqhGiQGE7GN/N/PYTaiOT+JEmKfoRDGMZSgFkpXYvQII+9CtVt+bOwVeJV5AqK9DoV756g0RkEcYkFBjT9dyU/Bw0SaFwWu5lBlMQYxhi19IYIjR+Pj93ys+tMuBhom3FxOfq74kcImMmUWA7I6CRWfZm4n9eN6Pwxs9lnGaEsVgsCjPFKeGz3/lAahSkJpaA0NLeysUINAiyCZVtCN7yy6ukdVnz3Jr3cFWt3xZxlNgpO2MXzGPXrM7uWYM1mWBj9sxe2ZuTOi/Ou/OxaF1zipkT9gfO5w81HY94</latexit><latexit sha1_base64="L7GVLX3zEiot9JRyFWQb1DEVmVI=">AAAB7nicbVDLSgNBEJz1GeMr6tHLYBA8hV0R9Bj04jGCeUCyhN5JbzJk9sFMrxCWfIQXD4p49Xu8+TdOkj1oYkFDUdVNd1eQKmnIdb+dtfWNza3t0k55d2//4LBydNwySaYFNkWiEt0JwKCSMTZJksJOqhGiQGE7GN/N/PYTaiOT+JEmKfoRDGMZSgFkpXYvQII+9CtVt+bOwVeJV5AqK9DoV756g0RkEcYkFBjT9dyU/Bw0SaFwWu5lBlMQYxhi19IYIjR+Pj93ys+tMuBhom3FxOfq74kcImMmUWA7I6CRWfZm4n9eN6Pwxs9lnGaEsVgsCjPFKeGz3/lAahSkJpaA0NLeysUINAiyCZVtCN7yy6ukdVnz3Jr3cFWt3xZxlNgpO2MXzGPXrM7uWYM1mWBj9sxe2ZuTOi/Ou/OxaF1zipkT9gfO5w81HY94</latexit>

b

<latexit sha1_base64="5TM62+gTIBC0ZKDPysfnMFUL6aw=">AAAB7nicbVDLSgNBEOz1GeMr6tHLYBA8hV0R9Bj04jGCeUCyhNlJbzJk9sFMrxCWfIQXD4p49Xu8+TdOkj1oYkFDUdVNd1eQKmnIdb+dtfWNza3t0k55d2//4LBydNwySaYFNkWiEt0JuEElY2ySJIWdVCOPAoXtYHw389tPqI1M4keapOhHfBjLUApOVmr3AiTeD/qVqltz52CrxCtIFQo0+pWv3iARWYQxCcWN6XpuSn7ONUmhcFruZQZTLsZ8iF1LYx6h8fP5uVN2bpUBCxNtKyY2V39P5DwyZhIFtjPiNDLL3kz8z+tmFN74uYzTjDAWi0VhphglbPY7G0iNgtTEEi60tLcyMeKaC7IJlW0I3vLLq6R1WfPcmvdwVa3fFnGU4BTO4AI8uIY63EMDmiBgDM/wCm9O6rw4787HonXNKWZO4A+czx82oY95</latexit><latexit sha1_base64="5TM62+gTIBC0ZKDPysfnMFUL6aw=">AAAB7nicbVDLSgNBEOz1GeMr6tHLYBA8hV0R9Bj04jGCeUCyhNlJbzJk9sFMrxCWfIQXD4p49Xu8+TdOkj1oYkFDUdVNd1eQKmnIdb+dtfWNza3t0k55d2//4LBydNwySaYFNkWiEt0JuEElY2ySJIWdVCOPAoXtYHw389tPqI1M4keapOhHfBjLUApOVmr3AiTeD/qVqltz52CrxCtIFQo0+pWv3iARWYQxCcWN6XpuSn7ONUmhcFruZQZTLsZ8iF1LYx6h8fP5uVN2bpUBCxNtKyY2V39P5DwyZhIFtjPiNDLL3kz8z+tmFN74uYzTjDAWi0VhphglbPY7G0iNgtTEEi60tLcyMeKaC7IJlW0I3vLLq6R1WfPcmvdwVa3fFnGU4BTO4AI8uIY63EMDmiBgDM/wCm9O6rw4787HonXNKWZO4A+czx82oY95</latexit><latexit sha1_base64="5TM62+gTIBC0ZKDPysfnMFUL6aw=">AAAB7nicbVDLSgNBEOz1GeMr6tHLYBA8hV0R9Bj04jGCeUCyhNlJbzJk9sFMrxCWfIQXD4p49Xu8+TdOkj1oYkFDUdVNd1eQKmnIdb+dtfWNza3t0k55d2//4LBydNwySaYFNkWiEt0JuEElY2ySJIWdVCOPAoXtYHw389tPqI1M4keapOhHfBjLUApOVmr3AiTeD/qVqltz52CrxCtIFQo0+pWv3iARWYQxCcWN6XpuSn7ONUmhcFruZQZTLsZ8iF1LYx6h8fP5uVN2bpUBCxNtKyY2V39P5DwyZhIFtjPiNDLL3kz8z+tmFN74uYzTjDAWi0VhphglbPY7G0iNgtTEEi60tLcyMeKaC7IJlW0I3vLLq6R1WfPcmvdwVa3fFnGU4BTO4AI8uIY63EMDmiBgDM/wCm9O6rw4787HonXNKWZO4A+czx82oY95</latexit><latexit sha1_base64="5TM62+gTIBC0ZKDPysfnMFUL6aw=">AAAB7nicbVDLSgNBEOz1GeMr6tHLYBA8hV0R9Bj04jGCeUCyhNlJbzJk9sFMrxCWfIQXD4p49Xu8+TdOkj1oYkFDUdVNd1eQKmnIdb+dtfWNza3t0k55d2//4LBydNwySaYFNkWiEt0JuEElY2ySJIWdVCOPAoXtYHw389tPqI1M4keapOhHfBjLUApOVmr3AiTeD/qVqltz52CrxCtIFQo0+pWv3iARWYQxCcWN6XpuSn7ONUmhcFruZQZTLsZ8iF1LYx6h8fP5uVN2bpUBCxNtKyY2V39P5DwyZhIFtjPiNDLL3kz8z+tmFN74uYzTjDAWi0VhphglbPY7G0iNgtTEEi60tLcyMeKaC7IJlW0I3vLLq6R1WfPcmvdwVa3fFnGU4BTO4AI8uIY63EMDmiBgDM/wCm9O6rw4787HonXNKWZO4A+czx82oY95</latexit>

E

0

-0.5

0.0

0.5

1.0

0.001

0.010

0.100

1

10

J (!)

<latexit sha1_base64="ifg8pn40Vf2r4e86F8Bxnb68/Eg=">AAAB+HicbVBNS8NAEN3Ur1o/GvXoJViEeimJCHosehFPFewHNCFstpN26WY37G6EGvpLvHhQxKs/xZv/xm2bg7Y+GHi8N8PMvChlVGnX/bZKa+sbm1vl7crO7t5+1T447CiRSQJtIpiQvQgrYJRDW1PNoJdKwEnEoBuNb2Z+9xGkooI/6EkKQYKHnMaUYG2k0K7ehX4EGtd9kcAQn4V2zW24czirxCtIDRVohfaXPxAkS4BrwrBSfc9NdZBjqSlhMK34mYIUkzEeQt9QjhNQQT4/fOqcGmXgxEKa4tqZq78ncpwoNUki05lgPVLL3kz8z+tnOr4KcsrTTAMni0VxxhwtnFkKzoBKIJpNDMFEUnOrQ0ZYYqJNVhUTgrf88irpnDc8t+HdX9Sa10UcZXSMTlAdeegSNdEtaqE2IihDz+gVvVlP1ov1bn0sWktWMXOE/sD6/AHrnpKY</latexit><latexit sha1_base64="ifg8pn40Vf2r4e86F8Bxnb68/Eg=">AAAB+HicbVBNS8NAEN3Ur1o/GvXoJViEeimJCHosehFPFewHNCFstpN26WY37G6EGvpLvHhQxKs/xZv/xm2bg7Y+GHi8N8PMvChlVGnX/bZKa+sbm1vl7crO7t5+1T447CiRSQJtIpiQvQgrYJRDW1PNoJdKwEnEoBuNb2Z+9xGkooI/6EkKQYKHnMaUYG2k0K7ehX4EGtd9kcAQn4V2zW24czirxCtIDRVohfaXPxAkS4BrwrBSfc9NdZBjqSlhMK34mYIUkzEeQt9QjhNQQT4/fOqcGmXgxEKa4tqZq78ncpwoNUki05lgPVLL3kz8z+tnOr4KcsrTTAMni0VxxhwtnFkKzoBKIJpNDMFEUnOrQ0ZYYqJNVhUTgrf88irpnDc8t+HdX9Sa10UcZXSMTlAdeegSNdEtaqE2IihDz+gVvVlP1ov1bn0sWktWMXOE/sD6/AHrnpKY</latexit><latexit sha1_base64="ifg8pn40Vf2r4e86F8Bxnb68/Eg=">AAAB+HicbVBNS8NAEN3Ur1o/GvXoJViEeimJCHosehFPFewHNCFstpN26WY37G6EGvpLvHhQxKs/xZv/xm2bg7Y+GHi8N8PMvChlVGnX/bZKa+sbm1vl7crO7t5+1T447CiRSQJtIpiQvQgrYJRDW1PNoJdKwEnEoBuNb2Z+9xGkooI/6EkKQYKHnMaUYG2k0K7ehX4EGtd9kcAQn4V2zW24czirxCtIDRVohfaXPxAkS4BrwrBSfc9NdZBjqSlhMK34mYIUkzEeQt9QjhNQQT4/fOqcGmXgxEKa4tqZq78ncpwoNUki05lgPVLL3kz8z+tnOr4KcsrTTAMni0VxxhwtnFkKzoBKIJpNDMFEUnOrQ0ZYYqJNVhUTgrf88irpnDc8t+HdX9Sa10UcZXSMTlAdeegSNdEtaqE2IihDz+gVvVlP1ov1bn0sWktWMXOE/sD6/AHrnpKY</latexit><latexit sha1_base64="ifg8pn40Vf2r4e86F8Bxnb68/Eg=">AAAB+HicbVBNS8NAEN3Ur1o/GvXoJViEeimJCHosehFPFewHNCFstpN26WY37G6EGvpLvHhQxKs/xZv/xm2bg7Y+GHi8N8PMvChlVGnX/bZKa+sbm1vl7crO7t5+1T447CiRSQJtIpiQvQgrYJRDW1PNoJdKwEnEoBuNb2Z+9xGkooI/6EkKQYKHnMaUYG2k0K7ehX4EGtd9kcAQn4V2zW24czirxCtIDRVohfaXPxAkS4BrwrBSfc9NdZBjqSlhMK34mYIUkzEeQt9QjhNQQT4/fOqcGmXgxEKa4tqZq78ncpwoNUki05lgPVLL3kz8z+tnOr4KcsrTTAMni0VxxhwtnFkKzoBKIJpNDMFEUnOrQ0ZYYqJNVhUTgrf88irpnDc8t+HdX9Sa10UcZXSMTlAdeegSNdEtaqE2IihDz+gVvVlP1ov1bn0sWktWMXOE/sD6/AHrnpKY</latexit>

!/!

c

<latexit sha1_base64="2eQrUChGm5cBz7D9uclHIS+N0XM=">AAAB+HicbVDLSgMxFL1TX7U+OurSTbAIruqMCLosunFZwT6gHYZMmmlDk8yQZIQ69EvcuFDErZ/izr8xbWehrQcu93DOveTmRCln2njet1NaW9/Y3CpvV3Z29/ar7sFhWyeZIrRFEp6oboQ15UzSlmGG026qKBYRp51ofDvzO49UaZbIBzNJaSDwULKYEWysFLrVfiLoEJ8vWkhCt+bVvTnQKvELUoMCzdD96g8SkgkqDeFY657vpSbIsTKMcDqt9DNNU0zGeEh7lkosqA7y+eFTdGqVAYoTZUsaNFd/b+RYaD0RkZ0U2Iz0sjcT//N6mYmvg5zJNDNUksVDccaRSdAsBTRgihLDJ5Zgopi9FZERVpgYm1XFhuAvf3mVtC/qvlf37y9rjZsijjIcwwmcgQ9X0IA7aEILCGTwDK/w5jw5L86787EYLTnFzhH8gfP5A4V7kvw=</latexit><latexit sha1_base64="2eQrUChGm5cBz7D9uclHIS+N0XM=">AAAB+HicbVDLSgMxFL1TX7U+OurSTbAIruqMCLosunFZwT6gHYZMmmlDk8yQZIQ69EvcuFDErZ/izr8xbWehrQcu93DOveTmRCln2njet1NaW9/Y3CpvV3Z29/ar7sFhWyeZIrRFEp6oboQ15UzSlmGG026qKBYRp51ofDvzO49UaZbIBzNJaSDwULKYEWysFLrVfiLoEJ8vWkhCt+bVvTnQKvELUoMCzdD96g8SkgkqDeFY657vpSbIsTKMcDqt9DNNU0zGeEh7lkosqA7y+eFTdGqVAYoTZUsaNFd/b+RYaD0RkZ0U2Iz0sjcT//N6mYmvg5zJNDNUksVDccaRSdAsBTRgihLDJ5Zgopi9FZERVpgYm1XFhuAvf3mVtC/qvlf37y9rjZsijjIcwwmcgQ9X0IA7aEILCGTwDK/w5jw5L86787EYLTnFzhH8gfP5A4V7kvw=</latexit><latexit sha1_base64="2eQrUChGm5cBz7D9uclHIS+N0XM=">AAAB+HicbVDLSgMxFL1TX7U+OurSTbAIruqMCLosunFZwT6gHYZMmmlDk8yQZIQ69EvcuFDErZ/izr8xbWehrQcu93DOveTmRCln2njet1NaW9/Y3CpvV3Z29/ar7sFhWyeZIrRFEp6oboQ15UzSlmGG026qKBYRp51ofDvzO49UaZbIBzNJaSDwULKYEWysFLrVfiLoEJ8vWkhCt+bVvTnQKvELUoMCzdD96g8SkgkqDeFY657vpSbIsTKMcDqt9DNNU0zGeEh7lkosqA7y+eFTdGqVAYoTZUsaNFd/b+RYaD0RkZ0U2Iz0sjcT//N6mYmvg5zJNDNUksVDccaRSdAsBTRgihLDJ5Zgopi9FZERVpgYm1XFhuAvf3mVtC/qvlf37y9rjZsijjIcwwmcgQ9X0IA7aEILCGTwDK/w5jw5L86787EYLTnFzhH8gfP5A4V7kvw=</latexit><latexit sha1_base64="2eQrUChGm5cBz7D9uclHIS+N0XM=">AAAB+HicbVDLSgMxFL1TX7U+OurSTbAIruqMCLosunFZwT6gHYZMmmlDk8yQZIQ69EvcuFDErZ/izr8xbWehrQcu93DOveTmRCln2njet1NaW9/Y3CpvV3Z29/ar7sFhWyeZIrRFEp6oboQ15UzSlmGG026qKBYRp51ofDvzO49UaZbIBzNJaSDwULKYEWysFLrVfiLoEJ8vWkhCt+bVvTnQKvELUoMCzdD96g8SkgkqDeFY657vpSbIsTKMcDqt9DNNU0zGeEh7lkosqA7y+eFTdGqVAYoTZUsaNFd/b+RYaD0RkZ0U2Iz0sjcT//N6mYmvg5zJNDNUksVDccaRSdAsBTRgihLDJ5Zgopi9FZERVpgYm1XFhuAvf3mVtC/qvlf37y9rjZsijjIcwwmcgQ9X0IA7aEILCGTwDK/w5jw5L86787EYLTnFzhH8gfP5A4V7kvw=</latexit>

(a)

(b)

(c)

<latexit sha1_base64="8MzdY9xWePsViGumrVRX3IPm9UE=">AAAB7HicbVBNS8NAEJ3Ur1q/qh69BIvgqSQi6LHoxWMFWwttKJvtpF262YTdiVBCf4MXD4p49Qd589+4bXPQ1gcDj/dmmJkXplIY8rxvp7S2vrG5Vd6u7Ozu7R9UD4/aJsk0xxZPZKI7ITMohcIWCZLYSTWyOJT4GI5vZ/7jE2ojEvVAkxSDmA2ViARnZKVWL0Ri/WrNq3tzuKvEL0gNCjT71a/eIOFZjIq4ZMZ0fS+lIGeaBJc4rfQygynjYzbErqWKxWiCfH7s1D2zysCNEm1LkTtXf0/kLDZmEoe2M2Y0MsveTPzP62YUXQe5UGlGqPhiUZRJlxJ39rk7EBo5yYkljGthb3X5iGnGyeZTsSH4yy+vkvZF3ffq/v1lrXFTxFGGEziFc/DhChpwB01oAQcBz/AKb45yXpx352PRWnKKmWP4A+fzB8PWjqQ=</latexit><latexit sha1_base64="8MzdY9xWePsViGumrVRX3IPm9UE=">AAAB7HicbVBNS8NAEJ3Ur1q/qh69BIvgqSQi6LHoxWMFWwttKJvtpF262YTdiVBCf4MXD4p49Qd589+4bXPQ1gcDj/dmmJkXplIY8rxvp7S2vrG5Vd6u7Ozu7R9UD4/aJsk0xxZPZKI7ITMohcIWCZLYSTWyOJT4GI5vZ/7jE2ojEvVAkxSDmA2ViARnZKVWL0Ri/WrNq3tzuKvEL0gNCjT71a/eIOFZjIq4ZMZ0fS+lIGeaBJc4rfQygynjYzbErqWKxWiCfH7s1D2zysCNEm1LkTtXf0/kLDZmEoe2M2Y0MsveTPzP62YUXQe5UGlGqPhiUZRJlxJ39rk7EBo5yYkljGthb3X5iGnGyeZTsSH4yy+vkvZF3ffq/v1lrXFTxFGGEziFc/DhChpwB01oAQcBz/AKb45yXpx352PRWnKKmWP4A+fzB8PWjqQ=</latexit><latexit sha1_base64="8MzdY9xWePsViGumrVRX3IPm9UE=">AAAB7HicbVBNS8NAEJ3Ur1q/qh69BIvgqSQi6LHoxWMFWwttKJvtpF262YTdiVBCf4MXD4p49Qd589+4bXPQ1gcDj/dmmJkXplIY8rxvp7S2vrG5Vd6u7Ozu7R9UD4/aJsk0xxZPZKI7ITMohcIWCZLYSTWyOJT4GI5vZ/7jE2ojEvVAkxSDmA2ViARnZKVWL0Ri/WrNq3tzuKvEL0gNCjT71a/eIOFZjIq4ZMZ0fS+lIGeaBJc4rfQygynjYzbErqWKxWiCfH7s1D2zysCNEm1LkTtXf0/kLDZmEoe2M2Y0MsveTPzP62YUXQe5UGlGqPhiUZRJlxJ39rk7EBo5yYkljGthb3X5iGnGyeZTsSH4yy+vkvZF3ffq/v1lrXFTxFGGEziFc/DhChpwB01oAQcBz/AKb45yXpx352PRWnKKmWP4A+fzB8PWjqQ=</latexit><latexit sha1_base64="8MzdY9xWePsViGumrVRX3IPm9UE=">AAAB7HicbVBNS8NAEJ3Ur1q/qh69BIvgqSQi6LHoxWMFWwttKJvtpF262YTdiVBCf4MXD4p49Qd589+4bXPQ1gcDj/dmmJkXplIY8rxvp7S2vrG5Vd6u7Ozu7R9UD4/aJsk0xxZPZKI7ITMohcIWCZLYSTWyOJT4GI5vZ/7jE2ojEvVAkxSDmA2ViARnZKVWL0Ri/WrNq3tzuKvEL0gNCjT71a/eIOFZjIq4ZMZ0fS+lIGeaBJc4rfQygynjYzbErqWKxWiCfH7s1D2zysCNEm1LkTtXf0/kLDZmEoe2M2Y0MsveTPzP62YUXQe5UGlGqPhiUZRJlxJ39rk7EBo5yYkljGthb3X5iGnGyeZTsSH4yy+vkvZF3ffq/v1lrXFTxFGGEziFc/DhChpwB01oAQcBz/AKb45yXpx352PRWnKKmWP4A+fzB8PWjqQ=</latexit>

Figure 1.

(a) Two-level system (TLS) is coupled to two environments (a, b) with inverse temperatures

β

a

and β

b

. (b) The reduced state dynamics of the TLS can be obtained from a zero-temperature

simulation of an extended environment containing negative frequency excitation modes and

temperature-dependent couplings. (c) The effective spectral density J

β

(

ω

)

encodes the principle

of detailed balance for absorption and emission of quanta between thermal transitions in the TLS. For

the Ohmic spectral density considered in this article, J

β

(

ω

)

becomes flat over the entire range

[

ω

c

, ω

c

]

as the temperature increases (β decreases). The plots shown are for ω

c

β

=

0.1 (Purple),ω

c

β

=

1

(9)

2.3. Chain mapping and chain coefficients

176

t

N

<latexit sha1_base64="Ujh5/GndTKwZOv2xKOQqzYpkn4Y=">AAAB6nicbVBNS8NAEJ3Ur1q/qh69LBbBU0lEqMeiF09S0X5AG8pmu2mXbjZhdyKU0J/gxYMiXv1F3vw3btsctPXBwOO9GWbmBYkUBl332ymsrW9sbhW3Szu7e/sH5cOjlolTzXiTxTLWnYAaLoXiTRQoeSfRnEaB5O1gfDPz209cGxGrR5wk3I/oUIlQMIpWesD+Xb9ccavuHGSVeDmpQI5Gv/zVG8QsjbhCJqkxXc9N0M+oRsEkn5Z6qeEJZWM65F1LFY248bP5qVNyZpUBCWNtSyGZq78nMhoZM4kC2xlRHJllbyb+53VTDK/8TKgkRa7YYlGYSoIxmf1NBkJzhnJiCWVa2FsJG1FNGdp0SjYEb/nlVdK6qHpu1bu/rNSv8ziKcAKncA4e1KAOt9CAJjAYwjO8wpsjnRfn3flYtBacfOYY/sD5/AExjI25</latexit><latexit sha1_base64="Ujh5/GndTKwZOv2xKOQqzYpkn4Y=">AAAB6nicbVBNS8NAEJ3Ur1q/qh69LBbBU0lEqMeiF09S0X5AG8pmu2mXbjZhdyKU0J/gxYMiXv1F3vw3btsctPXBwOO9GWbmBYkUBl332ymsrW9sbhW3Szu7e/sH5cOjlolTzXiTxTLWnYAaLoXiTRQoeSfRnEaB5O1gfDPz209cGxGrR5wk3I/oUIlQMIpWesD+Xb9ccavuHGSVeDmpQI5Gv/zVG8QsjbhCJqkxXc9N0M+oRsEkn5Z6qeEJZWM65F1LFY248bP5qVNyZpUBCWNtSyGZq78nMhoZM4kC2xlRHJllbyb+53VTDK/8TKgkRa7YYlGYSoIxmf1NBkJzhnJiCWVa2FsJG1FNGdp0SjYEb/nlVdK6qHpu1bu/rNSv8ziKcAKncA4e1KAOt9CAJjAYwjO8wpsjnRfn3flYtBacfOYY/sD5/AExjI25</latexit><latexit sha1_base64="Ujh5/GndTKwZOv2xKOQqzYpkn4Y=">AAAB6nicbVBNS8NAEJ3Ur1q/qh69LBbBU0lEqMeiF09S0X5AG8pmu2mXbjZhdyKU0J/gxYMiXv1F3vw3btsctPXBwOO9GWbmBYkUBl332ymsrW9sbhW3Szu7e/sH5cOjlolTzXiTxTLWnYAaLoXiTRQoeSfRnEaB5O1gfDPz209cGxGrR5wk3I/oUIlQMIpWesD+Xb9ccavuHGSVeDmpQI5Gv/zVG8QsjbhCJqkxXc9N0M+oRsEkn5Z6qeEJZWM65F1LFY248bP5qVNyZpUBCWNtSyGZq78nMhoZM4kC2xlRHJllbyb+53VTDK/8TKgkRa7YYlGYSoIxmf1NBkJzhnJiCWVa2FsJG1FNGdp0SjYEb/nlVdK6qHpu1bu/rNSv8ziKcAKncA4e1KAOt9CAJjAYwjO8wpsjnRfn3flYtBacfOYY/sD5/AExjI25</latexit><latexit sha1_base64="Ujh5/GndTKwZOv2xKOQqzYpkn4Y=">AAAB6nicbVBNS8NAEJ3Ur1q/qh69LBbBU0lEqMeiF09S0X5AG8pmu2mXbjZhdyKU0J/gxYMiXv1F3vw3btsctPXBwOO9GWbmBYkUBl332ymsrW9sbhW3Szu7e/sH5cOjlolTzXiTxTLWnYAaLoXiTRQoeSfRnEaB5O1gfDPz209cGxGrR5wk3I/oUIlQMIpWesD+Xb9ccavuHGSVeDmpQI5Gv/zVG8QsjbhCJqkxXc9N0M+oRsEkn5Z6qeEJZWM65F1LFY248bP5qVNyZpUBCWNtSyGZq78nMhoZM4kC2xlRHJllbyb+53VTDK/8TKgkRa7YYlGYSoIxmf1NBkJzhnJiCWVa2FsJG1FNGdp0SjYEb/nlVdK6qHpu1bu/rNSv8ziKcAKncA4e1KAOt9CAJjAYwjO8wpsjnRfn3flYtBacfOYY/sD5/AExjI25</latexit>

!

N

<latexit sha1_base64="UUjx/3S6j/PNLtIr/Uag01pO+Pk=">AAAB73icbVA9SwNBEJ2LXzF+RS1tFoNgFe5E0DJoYyURTAwkR9jbzCVLdvfO3T0hhPwJGwtFbP07dv4bN8kVmvhg4PHeDDPzolRwY33/2yusrK6tbxQ3S1vbO7t75f2DpkkyzbDBEpHoVkQNCq6wYbkV2Eo1UhkJfIiG11P/4Qm14Ym6t6MUQ0n7isecUeukVieR2Kfd22654lf9GcgyCXJSgRz1bvmr00tYJlFZJqgx7cBPbTim2nImcFLqZAZTyoa0j21HFZVowvHs3gk5cUqPxIl2pSyZqb8nxlQaM5KR65TUDsyiNxX/89qZjS/DMVdpZlGx+aI4E8QmZPo86XGNzIqRI5Rp7m4lbEA1ZdZFVHIhBIsvL5PmWTXwq8HdeaV2lcdRhCM4hlMI4AJqcAN1aAADAc/wCm/eo/fivXsf89aCl88cwh94nz/le4/c</latexit><latexit sha1_base64="UUjx/3S6j/PNLtIr/Uag01pO+Pk=">AAAB73icbVA9SwNBEJ2LXzF+RS1tFoNgFe5E0DJoYyURTAwkR9jbzCVLdvfO3T0hhPwJGwtFbP07dv4bN8kVmvhg4PHeDDPzolRwY33/2yusrK6tbxQ3S1vbO7t75f2DpkkyzbDBEpHoVkQNCq6wYbkV2Eo1UhkJfIiG11P/4Qm14Ym6t6MUQ0n7isecUeukVieR2Kfd22654lf9GcgyCXJSgRz1bvmr00tYJlFZJqgx7cBPbTim2nImcFLqZAZTyoa0j21HFZVowvHs3gk5cUqPxIl2pSyZqb8nxlQaM5KR65TUDsyiNxX/89qZjS/DMVdpZlGx+aI4E8QmZPo86XGNzIqRI5Rp7m4lbEA1ZdZFVHIhBIsvL5PmWTXwq8HdeaV2lcdRhCM4hlMI4AJqcAN1aAADAc/wCm/eo/fivXsf89aCl88cwh94nz/le4/c</latexit><latexit sha1_base64="UUjx/3S6j/PNLtIr/Uag01pO+Pk=">AAAB73icbVA9SwNBEJ2LXzF+RS1tFoNgFe5E0DJoYyURTAwkR9jbzCVLdvfO3T0hhPwJGwtFbP07dv4bN8kVmvhg4PHeDDPzolRwY33/2yusrK6tbxQ3S1vbO7t75f2DpkkyzbDBEpHoVkQNCq6wYbkV2Eo1UhkJfIiG11P/4Qm14Ym6t6MUQ0n7isecUeukVieR2Kfd22654lf9GcgyCXJSgRz1bvmr00tYJlFZJqgx7cBPbTim2nImcFLqZAZTyoa0j21HFZVowvHs3gk5cUqPxIl2pSyZqb8nxlQaM5KR65TUDsyiNxX/89qZjS/DMVdpZlGx+aI4E8QmZPo86XGNzIqRI5Rp7m4lbEA1ZdZFVHIhBIsvL5PmWTXwq8HdeaV2lcdRhCM4hlMI4AJqcAN1aAADAc/wCm/eo/fivXsf89aCl88cwh94nz/le4/c</latexit><latexit sha1_base64="UUjx/3S6j/PNLtIr/Uag01pO+Pk=">AAAB73icbVA9SwNBEJ2LXzF+RS1tFoNgFe5E0DJoYyURTAwkR9jbzCVLdvfO3T0hhPwJGwtFbP07dv4bN8kVmvhg4PHeDDPzolRwY33/2yusrK6tbxQ3S1vbO7t75f2DpkkyzbDBEpHoVkQNCq6wYbkV2Eo1UhkJfIiG11P/4Qm14Ym6t6MUQ0n7isecUeukVieR2Kfd22654lf9GcgyCXJSgRz1bvmr00tYJlFZJqgx7cBPbTim2nImcFLqZAZTyoa0j21HFZVowvHs3gk5cUqPxIl2pSyZqb8nxlQaM5KR65TUDsyiNxX/89qZjS/DMVdpZlGx+aI4E8QmZPo86XGNzIqRI5Rp7m4lbEA1ZdZFVHIhBIsvL5PmWTXwq8HdeaV2lcdRhCM4hlMI4AJqcAN1aAADAc/wCm/eo/fivXsf89aCl88cwh94nz/le4/c</latexit>

<latexit sha1_base64="qAsUf/1IAlAQB3I2YF1C2veiXKU=">AAAB7XicbVDLSgNBEOyNrxhfUY9eBoPgKeyKoMegF48RzAOSJfROJsmY2dlhZlYIS/7BiwdFvPo/3vwbJ8keNLGgoajqprsrUoIb6/vfXmFtfWNzq7hd2tnd2z8oHx41TZJqyho0EYluR2iY4JI1LLeCtZVmGEeCtaLx7cxvPTFteCIf7ESxMMah5ANO0Tqp2R2jUtgrV/yqPwdZJUFOKpCj3it/dfsJTWMmLRVoTCfwlQ0z1JZTwaalbmqYQjrGIes4KjFmJszm107JmVP6ZJBoV9KSufp7IsPYmEkcuc4Y7cgsezPxP6+T2sF1mHGpUsskXSwapILYhMxeJ32uGbVi4ghSzd2thI5QI7UuoJILIVh+eZU0L6qBXw3uLyu1mzyOIpzAKZxDAFdQgzuoQwMoPMIzvMKbl3gv3rv3sWgtePnMMfyB9/kDliyPHw==</latexit><latexit sha1_base64="qAsUf/1IAlAQB3I2YF1C2veiXKU=">AAAB7XicbVDLSgNBEOyNrxhfUY9eBoPgKeyKoMegF48RzAOSJfROJsmY2dlhZlYIS/7BiwdFvPo/3vwbJ8keNLGgoajqprsrUoIb6/vfXmFtfWNzq7hd2tnd2z8oHx41TZJqyho0EYluR2iY4JI1LLeCtZVmGEeCtaLx7cxvPTFteCIf7ESxMMah5ANO0Tqp2R2jUtgrV/yqPwdZJUFOKpCj3it/dfsJTWMmLRVoTCfwlQ0z1JZTwaalbmqYQjrGIes4KjFmJszm107JmVP6ZJBoV9KSufp7IsPYmEkcuc4Y7cgsezPxP6+T2sF1mHGpUsskXSwapILYhMxeJ32uGbVi4ghSzd2thI5QI7UuoJILIVh+eZU0L6qBXw3uLyu1mzyOIpzAKZxDAFdQgzuoQwMoPMIzvMKbl3gv3rv3sWgtePnMMfyB9/kDliyPHw==</latexit><latexit sha1_base64="qAsUf/1IAlAQB3I2YF1C2veiXKU=">AAAB7XicbVDLSgNBEOyNrxhfUY9eBoPgKeyKoMegF48RzAOSJfROJsmY2dlhZlYIS/7BiwdFvPo/3vwbJ8keNLGgoajqprsrUoIb6/vfXmFtfWNzq7hd2tnd2z8oHx41TZJqyho0EYluR2iY4JI1LLeCtZVmGEeCtaLx7cxvPTFteCIf7ESxMMah5ANO0Tqp2R2jUtgrV/yqPwdZJUFOKpCj3it/dfsJTWMmLRVoTCfwlQ0z1JZTwaalbmqYQjrGIes4KjFmJszm107JmVP6ZJBoV9KSufp7IsPYmEkcuc4Y7cgsezPxP6+T2sF1mHGpUsskXSwapILYhMxeJ32uGbVi4ghSzd2thI5QI7UuoJILIVh+eZU0L6qBXw3uLyu1mzyOIpzAKZxDAFdQgzuoQwMoPMIzvMKbl3gv3rv3sWgtePnMMfyB9/kDliyPHw==</latexit><latexit sha1_base64="qAsUf/1IAlAQB3I2YF1C2veiXKU=">AAAB7XicbVDLSgNBEOyNrxhfUY9eBoPgKeyKoMegF48RzAOSJfROJsmY2dlhZlYIS/7BiwdFvPo/3vwbJ8keNLGgoajqprsrUoIb6/vfXmFtfWNzq7hd2tnd2z8oHx41TZJqyho0EYluR2iY4JI1LLeCtZVmGEeCtaLx7cxvPTFteCIf7ESxMMah5ANO0Tqp2R2jUtgrV/yqPwdZJUFOKpCj3it/dfsJTWMmLRVoTCfwlQ0z1JZTwaalbmqYQjrGIes4KjFmJszm107JmVP6ZJBoV9KSufp7IsPYmEkcuc4Y7cgsezPxP6+T2sF1mHGpUsskXSwapILYhMxeJ32uGbVi4ghSzd2thI5QI7UuoJILIVh+eZU0L6qBXw3uLyu1mzyOIpzAKZxDAFdQgzuoQwMoPMIzvMKbl3gv3rv3sWgtePnMMfyB9/kDliyPHw==</latexit>

T=0K

T=0K

+E

-E

0

T=0K

Figure 2.

The positive and negative energy modes of each extended environment are mapped onto

1D chains with nearest-neighbour hopping, each coupled by their first site to the TLS with coupling

strength κ. The chain parameters e

n

and t

n

are determined such that the eigen-modes of the chains are

the original modes of the extended environments. The 1D geometry of the transformed system and the

fact that the chain modes all start in their vacuum states, means the system-environment state can be

described by a single (pure) MPS.

Following this transformation a further step is required to facilitate efficient simulation of the

many-body system+environment wave-function. This is to apply a unitary transformation to the

bath modes which converts the star-like geometry of H

ext

I

into a chain-like geometry, thus allowing

the use of Matrix-Product-State (MPS) methods [

11

,

43

,

44

] (see Figure

2

). We thus define new modes

c

(†)

n

=

R

−∞

U

n

(

ω

)

a

(†)

ω

, known as chain modes, via the unitary transformation U

n

(

ω

) =

q

J

β

(

ω

)

p

n

(

ω

)

where p

n

(

ω

)

are orthonormal polynomials with respect to the measure dω J

β

(

ω

)

. Thanks to the three

term recurrence relations associated with all orthonormal polynomials p

n

(

ω

)

[

43

], only one of these

new modes, n

=

1, will be coupled to the system, while all other chain modes will be coupled only to

their nearest neighbours [

43

]. Our interaction and bath Hamiltonians thus become

H

chain

I

=

κ AS

(

c

1

+

c

1

)

,

H

chain

E

=

n=1

en

c

n

c

n

+

n=1

(

t

n

c

n

c

n+1

+

h.c

)

.

(19)

The chain coefficients appearing in eq.

19

are related to the three-term recurrence parameters of the

177

orthonormal polynomials and can be computed using standard numerical techniques [

43

]. Since the

178

initial state of the bath was the vacuum state, it is unaffected by the chain transformation. We briefly

(10)

note the evolution of the asymptotic values of the chain parameters, as illustrated in Figure

3

. For a

180

smooth spectral density with a hard cut-off, it is has been rigorously proven that e

n

ωc

/2, t

n

ωc

/4

181

as n

∞ [

45

]. Figure

3

shows the dramatic changes in these asymptotic values as the temperature

182

is increased, which - from the numerical results - appear to be e

n

0, t

n

ω

c

/2 as n

∞ and

183

β

0. This can be naturally understood from the behaviour of the effective spectral functions J

β

(

ω

)

184

with increasing temperature, as illustrated in Figure

1

c. The spectral functions become symmetric and

185

have finite values over the whole domain

[−

ωc

, ω

c

]

. The asymptotic spectrum of the chain modes

186

thus has a bandwidth of 2ω

c

centred on ω

=

0, which, for a uniform hopping chain, requires the

187

numerically observed asymptotic chain parameters. In the particular case of the Ohmic environment

188

at high temperatures, it can easily be seen that J

β

(

ω

)

tends to a constant and so will have a chain

189

representation derived from the classical Legendre polynomials [

45

].

190

We have thus arrived at a formulation of the problem of finite-temperature open systems in which

191

the many-body environmental state is initialised as a pure product of trivial ground states, whilst

192

the effects of thermal fluctuations and populations are encoded in the Hamiltonian chain parameters

193

and system-chain coupling. These parameters must be determined once for each temperature but

194

- in principle - the actual simulation of the many-body dynamics is now no more complex than a

195

zero-temperature simulation!

(11)

●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●

■■■■■■■■

■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■

◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆

▲▲

▲▲

▲▲

▲▲

▲▲

▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲

20

40

60

80

100

0.25

0.30

0.35

0.40

0.45

0.50

●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●

■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■

◆◆◆◆◆◆

◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆◆

▲▲

▲▲▲

▲▲

▲▲

▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲

20

40

60

80

100

0.1

0.2

0.3

0.4

0.5

0.6

0.7

<latexit sha1_base64="DA8OeZ6uP+UVw2b+b+QqqhRzClw=">AAACBHicbVBNS8NAEN34WetX1GMvwSJ4Kokoeix68VjBfkATwmY7aZdudsPuRighBy/+FS8eFPHqj/Dmv3Hb5qCtDwYe780wMy9KGVXadb+tldW19Y3NylZ1e2d3b98+OOwokUkCbSKYkL0IK2CUQ1tTzaCXSsBJxKAbjW+mfvcBpKKC3+tJCkGCh5zGlGBtpNCu+bHEJPchVZQZgRe5LxIY4pAUoV13G+4MzjLxSlJHJVqh/eUPBMkS4JowrFTfc1Md5FhqShgUVT9TkGIyxkPoG8pxAirIZ08UzolRBk4spCmunZn6eyLHiVKTJDKdCdYjtehNxf+8fqbjqyCnPM00cDJfFGfM0cKZJuIMqASi2cQQTCQ1tzpkhE0q2uRWNSF4iy8vk85Zw7touHfn9eZ1GUcF1dAxOkUeukRNdItaqI0IekTP6BW9WU/Wi/VufcxbV6xy5gj9gfX5A/ZImO8=</latexit>

n

!

c

<latexit sha1_base64="7nZ6ggX0n8pSx85sae+cCUMRrBw=">AAAB/XicbVDLSsNAFJ3UV62v+Ni5GSyCq5KIosuiG5cVbC00IUymk3boPMLMRKgh+CtuXCji1v9w5984bbPQ1gMXDufcy733xCmj2njet1NZWl5ZXauu1zY2t7Z33N29jpaZwqSNJZOqGyNNGBWkbahhpJsqgnjMyH08up749w9EaSrFnRmnJORoIGhCMTJWityDIFEI5yYSRR5ITgYowkXk1r2GNwVcJH5J6qBEK3K/gr7EGSfCYIa07vleasIcKUMxI0UtyDRJER6hAelZKhAnOsyn1xfw2Cp9mEhlSxg4VX9P5IhrPeax7eTIDPW8NxH/83qZSS7DnIo0M0Tg2aIkY9BIOIkC9qki2LCxJQgram+FeIhsHMYGVrMh+PMvL5LOacM/b3i3Z/XmVRlHFRyCI3ACfHABmuAGtEAbYPAInsEreHOenBfn3fmYtVaccmYf/IHz+QNRLZXH</latexit>

t

n

!

c

<latexit sha1_base64="F1SstRATZTWwDwZvBN806C5UjPA=">AAAB6HicbVBNS8NAEJ3Ur1q/qh69LBbBU0lE0WPRi8cW7Ae0oWy2k3btZhN2N0IJ/QVePCji1Z/kzX/jts1BWx8MPN6bYWZekAiujet+O4W19Y3NreJ2aWd3b/+gfHjU0nGqGDZZLGLVCahGwSU2DTcCO4lCGgUC28H4bua3n1BpHssHM0nQj+hQ8pAzaqzUkP1yxa26c5BV4uWkAjnq/fJXbxCzNEJpmKBadz03MX5GleFM4LTUSzUmlI3pELuWShqh9rP5oVNyZpUBCWNlSxoyV39PZDTSehIFtjOiZqSXvZn4n9dNTXjjZ1wmqUHJFovCVBATk9nXZMAVMiMmllCmuL2VsBFVlBmbTcmG4C2/vEpaF1Xvquo2Liu12zyOIpzAKZyDB9dQg3uoQxMYIDzDK7w5j86L8+58LFoLTj5zDH/gfP4A2GOM9g==</latexit>

n

<latexit sha1_base64="F1SstRATZTWwDwZvBN806C5UjPA=">AAAB6HicbVBNS8NAEJ3Ur1q/qh69LBbBU0lE0WPRi8cW7Ae0oWy2k3btZhN2N0IJ/QVePCji1Z/kzX/jts1BWx8MPN6bYWZekAiujet+O4W19Y3NreJ2aWd3b/+gfHjU0nGqGDZZLGLVCahGwSU2DTcCO4lCGgUC28H4bua3n1BpHssHM0nQj+hQ8pAzaqzUkP1yxa26c5BV4uWkAjnq/fJXbxCzNEJpmKBadz03MX5GleFM4LTUSzUmlI3pELuWShqh9rP5oVNyZpUBCWNlSxoyV39PZDTSehIFtjOiZqSXvZn4n9dNTXjjZ1wmqUHJFovCVBATk9nXZMAVMiMmllCmuL2VsBFVlBmbTcmG4C2/vEpaF1Xvquo2Liu12zyOIpzAKZyDB9dQg3uoQxMYIDzDK7w5j86L8+58LFoLTj5zDH/gfP4A2GOM9g==</latexit>

n

<latexit sha1_base64="pGQCL8zuAyPx6Iuh1igf1XXE2mo=">AAAB/XicbVBNS8NAEN3Ur1q/6sfNS7AInkoiil6EohePFewHNCFstpN26WYTdidCLcW/4sWDIl79H978N27bHLT1wcDjvRlm5oWp4Bod59sqLC2vrK4V10sbm1vbO+XdvaZOMsWgwRKRqHZINQguoYEcBbRTBTQOBbTCwc3Ebz2A0jyR9zhMwY9pT/KIM4pGCsoHXhJDjwbMCwHplcdlhMOgXHGqzhT2InFzUiE56kH5y+smLItBIhNU647rpOiPqELOBIxLXqYhpWxAe9AxVNIYtD+aXj+2j43StaNEmZJoT9XfEyMaaz2MQ9MZU+zreW8i/ud1Mowu/RGXaYYg2WxRlAkbE3sShd3lChiKoSGUKW5utVmfKsrQBFYyIbjzLy+S5mnVPa86d2eV2nUeR5EckiNyQlxyQWrkltRJgzDySJ7JK3mznqwX6936mLUWrHxmn/yB9fkDpaeVWQ==</latexit>

!

c

=

1

<latexit sha1_base64="aaVGka5VxVzFD6e+a4vb2Mibvqo=">AAAB+nicbVBNS8NAEN3Ur1q/Uj16CRbBU0lE0YtQ9OKxgv2AJoTNdtIu3eyG3Y1SYn+KFw+KePWXePPfuG1z0NYHA4/3ZpiZF6WMKu2631ZpZXVtfaO8Wdna3tnds6v7bSUySaBFBBOyG2EFjHJoaaoZdFMJOIkYdKLRzdTvPIBUVPB7PU4hSPCA05gSrI0U2lVfJDDAIfEj0PjKc93Qrrl1dwZnmXgFqaECzdD+8vuCZAlwTRhWque5qQ5yLDUlDCYVP1OQYjLCA+gZynECKshnp0+cY6P0nVhIU1w7M/X3RI4TpcZJZDoTrIdq0ZuK/3m9TMeXQU55mmngZL4ozpijhTPNwelTCUSzsSGYSGpudcgQS0y0SatiQvAWX14m7dO6d153785qjesijjI6REfoBHnoAjXQLWqiFiLoET2jV/RmPVkv1rv1MW8tWcXMAfoD6/MHKTuTRg==</latexit>

!

c

= 100

<latexit sha1_base64="X37rup26hGpmBj33vsl16Fc7/WY=">AAAB+XicbVBNS8NAEN3Ur1q/oh69LBbBU0nEoheh6MVjBWsLTQib7bRdursJu5tCCf0nXjwo4tV/4s1/47bNQVsfDDzem2FmXpxypo3nfTultfWNza3ydmVnd2//wD08etJJpii0aMIT1YmJBs4ktAwzHDqpAiJiDu14dDfz22NQmiXy0UxSCAUZSNZnlBgrRa4bJAIGJKJBDIbc1L3IrXo1bw68SvyCVFGBZuR+Bb2EZgKkoZxo3fW91IQ5UYZRDtNKkGlICR2RAXQtlUSADvP55VN8ZpUe7ifKljR4rv6eyInQeiJi2ymIGeplbyb+53Uz078OcybTzICki0X9jGOT4FkMuMcUUMMnlhCqmL0V0yFRhBobVsWG4C+/vEqeLmp+veY9XFYbt0UcZXSCTtE58tEVaqB71EQtRNEYPaNX9Obkzovz7nwsWktOMXOM/sD5/AG7opMQ</latexit>

!

c

= 50

<latexit sha1_base64="01Q3r3635SJynl38NkFtEUo654o=">AAAB+XicbVBNS8NAEN34WetX1KOXxSJ4KklR9CIUvXisYD+gCWWznbRLd7Nhd1Moof/EiwdFvPpPvPlv3LY5aOuDgcd7M8zMi1LOtPG8b2dtfWNza7u0U97d2z84dI+OW1pmikKTSi5VJyIaOEugaZjh0EkVEBFxaEej+5nfHoPSTCZPZpJCKMggYTGjxFip57qBFDAgPRpEYMhtzeu5Fa/qzYFXiV+QCirQ6LlfQV/STEBiKCdad30vNWFOlGGUw7QcZBpSQkdkAF1LEyJAh/n88ik+t0ofx1LZSgyeq78nciK0nojIdgpihnrZm4n/ed3MxDdhzpI0M5DQxaI449hIPIsB95kCavjEEkIVs7diOiSKUGPDKtsQ/OWXV0mrVvWvqt7jZaV+V8RRQqfoDF0gH12jOnpADdREFI3RM3pFb07uvDjvzseidc0pZk7QHzifP7cTkw0=</latexit>

!

c

= 20

Figure 3.

Site energies e

n

(a) and hopping amplitudes t

n

(b) as a function of chain distance n at different

environment temperatures

2.4. Spin-boson model across the complete α

β space

197

In this section, we numerically verify that the finite-temperature approach set out in Sections

198

2.2

&

2.3

captures the correct non-perturbative behaviour in the single-bath spin-boson model. This

199

will be illustrated with a few explicit examples, but the key result of this section is the creation of a

200

comprehensive data set for the Ohmic spin-boson model that allows arbitrary TLS initial conditions to

201

be propagated in real-time and over a large area of α

β

space. This data set has been made freely

202

available online in citable form and can be used to benchmark other methods and applications [

46

].

203

Figure

4

a,b shows the temporal decay of an initially polarised spin

h

σ

z

(

0

)i = +

1 towards thermal

204

equilibrium for varying coupling strengths α and inverse temperatures β. The TLS energy splitting

(12)

was ω

0

=

0.2ω

c

. The key result in Figure

4

b is the dependence of the thermalized spin polarization at

206

long times. In a simple, perturbative rate equation treatment, this final polarization would be set by

207

the energy gap ω

0

and the temperature, according to the Gibbs-Boltzmann distribution

208

h

σ

z

i

β

=

(

1

e

−βω

0

)

(

1

+

e

−βω

0

)

.

(20)

The coupling strength α would only alter the rate at which this thermal distribution is reached.

209

However, Figure

4

a shows a growing dependence of the final polarization on the coupling strength,

210

suggesting a non-perturbative effect. This is indeed the case: strong coupling leads to polaron

211

formation and non-perturbative renormalisation of the TLS energy gap ω

0

. According to the variational

212

theory of Silbey and Harris [

47

], the renormalized gap ω

r

is approximately given by

213

ωr

=

ω

0



ω0

ωc



1

α

α

,

(21)

in the so-called scaling limit in which ω

c

is much larger than all other energy scales in the problem.

This renormalisation is highly non-perturbative, and can completely close the TLS energy gap at a

critical coupling α

c

=

1 [

2

]. Replacing ω

0

with the the renormalized energy gaps in Eq.

20

,

h

σz

i

β

is

given

h

σz

i

β

=



ω

0

ω

c



1

α

α

(

1

e

−βω

r

)

(

1

+

e

−βω

r

)

.

(22)

where the prefactor in accounts for the suppressed expectation values of σ

z

in the polaronic eigenbasis.

214

Figure

5

shows this analytical prediction as a function of temperature, compared to the results

215

extracted from the real-time dynamics. As mentioned above, most analytical predictions for the SBM

216

are obtained deep in the scaling limit, while numerical results necessarily involve only moderately

217

large values of ω

c

. When comparing results, it is common in the literature to evaluate analytical

218

expressions with a re-scaled coupling strength ˜α

=

cα to account for this [

48

50

], which we have

219

applied in Figure

5

. We found that a constant factor c

=

0.66 gave excellent agreement across the

220

parameter space for both one and two-bath SBMs, as shown in the inset of Figure

5

.

Références

Documents relatifs

We can analyze fermions at nonzero temperature by using boundary conditions which are antiperiodic in the time direction (this leads to the correct Fermi-Dirac

be too high for them to be still usable with typical gate-driver designs. 3), at the end of the first series of low-voltage gate sweeping, the measured equivalent

On the syntactic level, the logic T-STIT is nothing but the extension of atemporal individual STIT by: (i) the future tense and past tense operators, and (ii) the operator of

On the other hand, comparison between the different transport models confirms the fact that the source terms in the momentum equation do dominate the transient response of the

choose first a random direction (+I or -I) for the stochastic magnetic field that is associated to the thermal noise and then a random number z to be compared to the flip

The flow features are obtained for axisymmetric tubes (DUCT) and a converging domain (CONV1), with transition from adherence to slip at the wall, using the so-called Stream-Tube

L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des