Nonperturbative environmental influence on dephasing

Palm, T.; Nalbach, P.

doi:10.1103/physreva.96.032105

Cited by 7 publications

(10 citation statements)

References 22 publications

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“…( 16), the qdependent coupling of noise is governed by ∆ 2 /(q 2 +∆ 2 ), the Lorentzian Q B dependent denominator determines the LC-filtered bandpass of the coupling, and ∆E/(1 − e −βB∆E ) is due to the bare thermal noise of the resistor. Thus, making the quality factor of the resonators Q B much larger in comparison to ∆E C /(∆E H − ∆E C ), the TLS couples essentially to one bath only at a time which helps us to ignore the possibilities of any unexpected behavior due to different noise sources [37,38]. This condition can be met for any Q B 1, unless the two resonators are nearly identical.…”

Section: Introductionmentioning

confidence: 99%

Supremacy of incoherent sudden cycles

et al. 2019

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We investigate theoretically a refrigerator based on a two-level system (TLS) coupled alternately to two different heat baths. Modulation of the coupling is achieved by tuning the level spacing of the TLS. We find that the TLS, which avoids quantum coherences, creates finite cooling power for one of the baths in sudden cycles, i.e. acts as a refrigerator even in the limit of infinite operation frequency. By contrast, the cycles that create quantum coherence in the sudden expansions and compressions lead to heating of both the baths. We propose a driving method that avoids creating coherence and thus restores the cooling in this system. We also discuss a physical realization of the cycle based on a superconducting qubit coupled to dissipative LC-resonators.

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Section: Introductionmentioning

confidence: 99%

Supremacy of incoherent sudden cycles

et al. 2019

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“…Typical quantum systems are subject to various environmental noise sources. If one of them is strongly influencing the quantum system, the others cannot be treated within weak coupling approaches either 12 . We have extended the numerically exact quasi-adiabatic path integral approach 13,14 which allows to determine the time dependent reduced statistical operator of a quantum system under the influence of multiple noise sources.…”

Section: Discussionmentioning

confidence: 99%

“…Standard methods can easily be extended to this problem. This approach fails to describe the dynamics correctly when the phenomenological treated noise is strongly coupled to the system 12 even at very weak coupling to the other noise sources.…”

Section: Introductionmentioning

confidence: 99%

Quasi-adiabatic path integral approach for quantum systems under the influence of multiple non-commuting fluctuations

Palm

Nalbach

2018

The Journal of Chemical Physics

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Quantum systems are typically subject to various environmental noise sources. Treating these environmental disturbances with a system-bath approach beyond weak coupling one must refer to numerical methods as, for example, the numerically exact quasi-adiabatic path integral approach. This approach, however, cannot treat baths which couple to the system via operators, which do not commute. We extend the quasi-adiabatic path integral approach by determining the time discrete influence functional for such non-commuting fluctuations and by modifying the propagation scheme accordingly. We test the extended quasi-adiabatic path integral approach by determining the time evolution of a quantum two-level system coupled to two independent bath via non-commuting operators. We show that convergent results can be obtained and agreement with analytical weak coupling results is achieved in the respective limits.

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“…Superdecoherence has been predicted in Refs. [7,15], and has been observed experimentally in an ion-trap quantum computer [20]. Although some states suffer superdecoherence, the probability of running into such a state during the course of an actual algorithm may be extremely small [17].…”

Section: Introductionmentioning

confidence: 95%

“…This model is exactly solvable, and at the same time broadly relevant because dephasing times are typically much shorter than relaxation times [7,15,12]. It should be noted, how-ever, that there are situations where it does not accurately describe the decoherence process because of non-perturbative effects [15,12]. If, in the dephasing model, each qubit is assumed to couple to its own, independent reservoir, the decoherence rate per qubit is constant.…”

Section: Introductionmentioning

confidence: 99%

Conditions for superdecoherence

Kattemölle

Wezel

2020

Quantum

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Decoherence is the main obstacle to quantum computation. The decoherence rate per qubit is typically assumed to be constant. It is known, however, that quantum registers coupling to a single reservoir can show a decoherence rate per qubit that increases linearly with the number of qubits. This effect has been referred to as superdecoherence, and has been suggested to pose a threat to the scalability of quantum computation. Here, we show that superdecoherence is absent when the spectrum of the single reservoir is continuous, rather than discrete. The reason of this absence, is that, as the number of qubits is increased, a quantum register inevitably becomes susceptible to an ever narrower bandwidth of frequencies in the reservoir. Furthermore, we show that for superdecoherence to occur in a reservoir with a discrete spectrum, one of the frequencies in the reservoir has to coincide exactly with the frequency the quantum register is most susceptible to. We thus fully resolve the conditions that determine the presence or absence of superdecoherence. We conclude that superdecoherence is easily avoidable in practical realizations of quantum computers.

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Nonperturbative environmental influence on dephasing

Cited by 7 publications

References 22 publications

Supremacy of incoherent sudden cycles

Supremacy of incoherent sudden cycles

Quasi-adiabatic path integral approach for quantum systems under the influence of multiple non-commuting fluctuations

Conditions for superdecoherence

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