Abstract

Systems that are driven out of thermal equilibrium typically dissipate random quantities of energy on microscopic scales. Crooks fluctuation theorem relates the distribution of these random work costs with the corresponding distribution for the reverse process. By an analysis that explicitly incorporates the energy reservoir that donates the energy, and the control system that implements the dynamic, we here obtain a quantum generalization of Crooks theorem that not only includes the energy changes in the reservoir, but the full description of its evolution, including coherences. This approach moreover opens up for generalizations of the concept of fluctuation relations. Here we introduce `conditional' fluctuation relations that are applicable to non-equilibrium systems, as well as approximate fluctuation relations that allow for the analysis of autonomous evolution generated by global time-independent Hamiltonians. We furthermore extend these notions to Markovian master equations, implicitly modeling the influence of the heat bath.

Highlights

  • Imagine a physical system with a Hamiltonian HS ðxÞ that depends on some external parameter x, e.g., electric or magnetic fields that we can vary at will

  • There are several reasons why it is useful to generalize the type of quantum fluctuation theorems that we have considered so far

  • This is in contrast to approaches where the purpose of the measurements is to generate classical outcomes and where the quantum fluctuation relations are based on the resulting probability distributions, much in the spirit of classical fluctuation relations

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Summary

INTRODUCTION

Imagine a physical system with a Hamiltonian HS ðxÞ that depends on some external parameter x, e.g., electric or magnetic fields that we can vary at will. We can push the system out of thermal equilibrium This would typically require work that may be dissipated because of interactions with the surrounding heat bath. The key is to explicitly model all degrees of freedom (d.o.f.) involved in the process This includes the control mechanism that implements the change of the external parameter, i.e., x in HS ðxÞ, as well as the “energy reservoir,”. The general theme of this investigation is to formulate fluctuation relations in terms of this induced evolution. To make this more concrete, let us briefly display the first of the fluctuation theorems that we will derive.

QUANTUM FLUCTUATION THEOREM
Intermediate version
Time reversals and time-reversal symmetry
Deriving the quantum Crooks relation
Diagonal and off-diagonal Crooks relations
Jarzynski equalities
Bounds on the work cost
Energy-translation invariance:
CONDITIONAL FLUCTUATION THEOREMS
Gibbs map and partition map
Conditional fluctuation relation
ALTERNATIVE FORMULATION
CORRELATED INITIAL STATES
Correlations between E and an external reference
APPROXIMATE FLUCTUATION RELATIONS
Approximate conditional fluctuation relations
Joint control system and energy reservoir
Fluctuation relations for time-reversal-symmetric thermal operations
Yet another extension
Condition on generators
Constructing generators
Decoupling again
Generators of thermal and time-reversal-symmetric thermal operations
Two coupled thermalizing spins
Free-energy differences
E Þ ð47Þ where the transition probabilities are fþ
Jaynes-Cummings model with dissipation
VIII. CONCLUSIONS AND OUTLOOK
Setting the stage
Global Hamiltonian H and global evolution V
Initial states
Induced channels on the energy reservoir
Conjugate CPMs
Derivation of an intermediate fluctuation relation
Mapping J
Control in fluctuation theorems vs control in thermal protocols
Remarks concerning Crooks operation time reversal and Petz recovery channel
Brief reminder of the standard notion of time reversals
What we require from time reversals
Characterization of T in finite dimensions
Induced channels
Unbounded HE
Decoupling of diagonals
Diagonal Crooks relations
Off-diagonal Crooks relations
Bound on the average energy loss in the reservoir
An example
Bound on “second law violations”
Bound for a closed cycle
Examples
The Gibbs map and partition map
Without time reversal
With time reversal
Generally no decoupling of diagonals
Nevertheless diagonal and off-diagonal conditional fluctuation relations
Global invariance
Issue with nonexponential generalizations of the Gibbs maps
General notion of approximate fluctuation relations
Joint control and energy reservoir
Comparisons
Conditional fluctuation relations again
An approximate version
Decoupling of diagonals again
Example of the approximate fluctuation relation
More widely applicable approximate fluctuation relations?
Detailed balance
Heat baths in the Gibbs state
Full Text
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