Quantum information processing and relativistic quantum fields

Benincasa, Dionigi M. T.; Borsten, L.; Buck, Michel; Dowker, Fay

doi:10.1088/0264-9381/31/7/075007

Cited by 60 publications

(77 citation statements)

References 29 publications

(67 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…1. Conclusion.-The notion of work distributions for localized operations on quantum fields is challenging because a) energy eigenstates are not localized and b) projective measurements cannot be allowed in a relativistic quantum theory [10][11][12]. The TPM scheme employed in the literature [5] is hence ill-defined in QFT, but we have shown that one can still make sense of it via the Ramsey scheme that was designed to measure TPM work distributions [16,17].…”

Section: A Second Hadamard Is Applied To the Qubitmentioning

confidence: 99%

“…Finally we discuss how, through either Crooks or Jarzynski's theorems, the proposed work distribution can be used as a new way of computing ratios of partition functions between field theories, potentially yielding simpler approaches to the problem than path integral methods.TPM work distributions and Ramsey scheme.-Consider a quantum field initially in an equilibrium KMS stateρ of temperature β −1 , which is driven out of equilibrium by a time-dependent HamiltonianĤ(t), turned arXiv:1902.03258v2 [quant-ph] 9 Oct 2019 2 on during an interval [0, T ]. The work distribution quantifies the work cost of the unitary process on the field U (T, 0) generated by the HamiltonianĤ(t).As discussed above projective measurements cannot be implemented in quantum fields because they are incompatible with relativistic causality [10][11][12]. Thus, the TPM scheme cannot be readily applied to processes involving quantum fields.…”

mentioning

confidence: 99%

See 1 more Smart Citation

Work Distributions on Quantum Fields

et al. 2019

View full text Add to dashboard Cite

We study the work cost of processes in quantum fields without the need of projective measurements, which are always ill-defined in quantum field theory. Inspired by interferometry schemes, we propose a work distribution that generalizes the two-point measurement scheme employed in quantum thermodynamics to the case of quantum fields and avoids the use of projective measurements. The distribution is calculated for local unitary processes performed on KMS (thermal) states of scalar fields. Crooks theorem and the Jarzynski equality are shown to be satisfied for a family of spatio-temporally localized unitaries, and some features of the resulting distributions are studied as functions of temperature and the degree of localization of the unitary operation. We show how the work fluctuations become much larger than the average as the process becomes more localized in both time and space.Introduction.-At microscopic scales average quantities no longer characterize completely the state of a system or the features of a thermodynamic process. There, stochastic or quantum fluctuations become relevant, being of the same order of magnitude as the expectation values [1][2][3]. It is therefore important to develop tools that allow us to study the properties of these fluctuations to fully understand thermodynamics at the small scales.One of the best studied quantities in this context is work of out-of-equilibrium processes, and its associated fluctuations. The notion of work is an empirical cornerstone of macroscopic equilibrium thermodynamics. However, work in microscopic quantum scenarios is a notoriously subtle concept (e.g., it cannot be associated to an observable [4]), and although there is no single definition of work distributions and work fluctuations in quantum theory, several possibilities have been proposed (see e.g., [5]). Perhaps the most established notion of work fluctuations is that defined through the Two-Point Measurement (TPM) scheme [6,7], where the work distribution of a process is obtained by performing two projective measurements of the system's energy, at the beginning and at the end of the process. The TPM formalism defines a work distribution with a number of desirable properties: it is linear on the input states, it agrees with the unambiguous classical definition for states diagonal in the energy eigenbasis, and it yields a number of fluctuation theorems in different contexts [1,7,8].An important caveat of this definition is that it cannot be straightforwardly generalized to processes involving quantum fields: projective measurements in quantum field theory (QFT) are incompatible with its relativistic nature. They cannot be localized [9], they can introduce ill-defined operations due to UV divergences and, among other serious problems, they enable superluminal signaling even in the most innocent scenarios [10]. For these reasons, it has been strongly argued that projective measurements should be banished from the formalism of any relativistic field theory [10][11][12]. However, quantum fields are cert...

show abstract

Section: A Second Hadamard Is Applied To the Qubitmentioning

confidence: 99%

mentioning

confidence: 99%

Work Distributions on Quantum Fields

et al. 2019

View full text Add to dashboard Cite

show abstract

“…(8), the second-order perturbative corrections ρ (2) T to the total system's final state ρ T are given by…”

Section: Appendix A: Integral Form Of the Channel Coefficientsmentioning

confidence: 99%

“…Concretely, as has been pointed out in [2,3], the naive use of a Jaynes-Cummings model with a single-mode approximation (i.e., considering a system of detectors which interact only with a single mode of the quantum field in a cavity) shows inconsistencies at these scales, in the sense that it would allow superluminal signaling. The occurrence of this problem is plausible, considering that a single mode is a completely nonlocal degree of freedom.…”

Section: Introductionmentioning

confidence: 99%

Quantum signaling in cavity QED

2014

View full text Add to dashboard Cite

We consider quantum signaling between two-level quantum systems in a cavity in the perturbative regime of the earliest possible arrival times of the signal. We present two main results: First, we find that, perhaps surprisingly, the analog of amplitude modulated signaling (Alice using her energy eigenstates |g , |e , as in the Fermi problem) is generally suboptimal for communication, namely, e.g., phase-modulated signaling (Alice using, e.g., {|+ , |− } states) overcomes the quantum noise already at a lower order in perturbation theory. Second, we study the effect of mode truncations that are commonly used in cavity QED on the modeling of the communication between two-level atoms. We show that, on general grounds, namely for causality to be preserved, the UV cutoff must scale at least polynomially with the desired accuracy of the predictions.

show abstract

“…The entanglement of created particles in curved spacetime and its applications such as quantum information protocols in the relativistic limit is well-known for understanding of the nature of the universe [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17]. The von Neumann entropy of created particles as a measure of entanglement is often applied to discover of the encoded information of spacetime [2,3].…”

Section: Introductionmentioning

confidence: 99%

Entropy Production in the Expanding Universe

Farahmand

Mohammadzadeh

2017

The 4th International Electronic Conference on Entropy and Its Applications

View full text Add to dashboard Cite

Abstract:The spacetime is basically curved and dynamical. Thus our knowledge of universe must be extended to a dynamical curved spacetime to understand the nature of the universe. The field theory in the curved spacetime has shown that the evolution of spacetime involving the field in the curved spacetime leads to particle creation. From another perspective, by employing thermodynamics to cosmology, we can learn about the source of current entropy content associated with the universe. From the quantum thermodynamics, it is clear that the inner friction stemming from the quantum fluctuations of the field can produce the entropy. Using this approach, the particle creation due to the expansion of spacetime beginning from the vacuum is shown as an entropic increase. Considering an asymptotically flat Robertson-Walker spacetime, the particle creation entropy is evaluated. Each special scale factor can be used to characterize the cosmic parameters. Thus, the dependence of particle creation entropy on the field parameters and the cosmic parameters allows us to recover information from the underlying structure of the spacetime. Also, by adding an entropy production, indicating the mutual information between created particle and spacetime, to this particle creation entropy, the well-known entanglement measure can obtained to investigate the entanglement of created particles. In fact, the entanglement entropy, measuring the mixedness of the primary state, is affected from the creation and the correlation of the particle.

show abstract

Quantum information processing and relativistic quantum fields

Cited by 60 publications

References 29 publications

Work Distributions on Quantum Fields

Work Distributions on Quantum Fields

Quantum signaling in cavity QED

Entropy Production in the Expanding Universe

Contact Info

Product

Resources

About