Fermi Problem with Artificial Atoms in Circuit QED

Sabín, Carlos; Rey, Marco del; García-Ripoll, Juan José; León, Juan

doi:10.1103/physrevlett.107.150402

Cited by 36 publications

(59 citation statements)

References 19 publications

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“…The expressions for C 2 , D 2 , A 4 , B 4 , P 2 , and P 4 are rather complex and are given in Appendix A where some interesting points about their mathematical form are also discussed. We can understand both the general structure of the channel and the form of the individual terms by discussing how they originate from (14).…”

Section: Settingmentioning

confidence: 99%

“…In fact, it is known that two localized and spacelike separated quantum systems can be made entangled by merely letting them interact with the field vacuum state. The systems get entangled because they swap entanglement from the vacuum rather than by interacting through the exchange of real field quanta (see, e.g., [5,[10][11][12][13][14][15]). The impact of curvature was studied in [16].…”

Section: Introductionmentioning

confidence: 99%

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Quantum signaling in cavity QED

2014

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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.

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Section: Settingmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Quantum signaling in cavity QED

2014

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“…Thus this dynamics is only important during the activation of the SQUID, a process that may be in the nanosecond regime. Therefore, if at t = 0 the system is in the initial state of |eg0 (see [17]) for the preparation of such a state) and then we measure the state of the qubit, our results show that a click of the detector could be as related to a self-excitation as to an absorption of a photon emitted by the source.…”

mentioning

confidence: 96%

“…For that case the situation gets more complicated, as there are interfering processes of orders 1 and 3 leading to that final state. This calculation has been the focus of a recent work [17]. The four diagrams contributing to |B 1 | 2 up to fourth order in perturbation theory can be seen in fig (3).…”

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confidence: 99%

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Short-time quantum detection: Probing quantum fluctuations

Rey¹,

Sabín²,

León³

2012

Phys. Rev. A

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In this work we study the information provided by a detector click on the state of an initially excited two level system. By computing the time evolution of the corresponding conditioned probability beyond the rotating wave approximation, as needed for short time analysis, we show that a click in the detector is related with the decay of the source only for long times of interaction. For short times, non-rotating wave approximation effects, like self-excitations of the detector, forbid a naïve interpretation of the detector readings. These effects might appear in circuit QED experiments.PACS numbers: 11.10.-z, 29.40.-n, 42.50.-p, 85.25.-j Quantum detection theory was created to study the behavior of detectors in presence of radiation [1]. Highly satisfactory up to date, it relies on the conspicuous rotating wave approximation (RWA), which neglects the so-called counterrotating terms, irrelevant in most cases. These terms give important contributions for strong atom-field couplings and very short times as compared to the system time scale, meaning that for any effect beyond RWA to be acknowledged our measurements must be very precise and the observation times quite fast. This is particularly problematic for Quantum Optics experiments, due to the very small matter-radiation coupling and the fact that observation times must be at the femtosecond scale for most cases (nanosecond for hyperfine qubits), which is ridiculously small for current experiments (∼ µs for trapped ions [2]).However, circuit QED [3] provides a framework in which those phenomena are accessible to explore. By using superconducting qubits as artificial atoms coupled to a transmission line, one gets a system which behaves analogously as a 1-D radiation-matter interaction in Quantum Optics, while working at the microwave frequency range [4]. In this setup, parameters can be easily tuned, and the coupling between qubits and transmission line can be modulated up to ultrastrong levels. [5,6] Besides, fast qubit state readout (∼ ns) is possible using a pulsed DC-SQUID scheme [7] .In those conditions, phenomena beyond RWA have already been reported [8], [9]. In this regime Glauber's theory is no longer valid and quantum detectors should be described by a non-RWA model.A counterintuitive direct consequence of the breakdown of the RWA is that a detector in its ground state interacting with the vacuum of the field has a certain probability of getting excited and emitting a photon. There is however not a real consensus on the physical reality of this effect. Introducing counterrotating terms is interpreted by some to be a problem as the processes described by those terms seem virtual. It seems counterintuitive to accept that a detector in a ground state in the vacuum could get excited. As a matter of fact, there have been attempts of suggesting effective detector models by imposing this phenomenon to be impossible [10].We should however point out here that there is no problem whatsoever with energy conservation, as unitary evolution of the states under a ...

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Harvesting entanglement by non-identical detectors with different energy gaps

Hu¹,

Zhang²,

Yu³

2022

J. High Energ. Phys.

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It has been shown that the vacuum state of a free quantum field is entangled and such vacuum entanglement can be harvested by a pair of initially uncorrelated detectors interacting locally with the vacuum field for a finite time. In this paper, we examine the entanglement harvesting phenomenon of two non-identical inertial detectors with different energy gaps locally interacting with massless scalar fields via a Gaussian switching function. We focus on how entanglement harvesting depends on the energy gap difference from two perspectives: the amount of entanglement harvested and the harvesting-achievable separation between the two detectors. In the sense of the amount of entanglement, we find that as long as the inter-detector separation is not too small with respect to the interaction duration parameter, two non-identical detectors could extract more entanglement from the vacuum state than the identical detectors. There exists an optimal value of the energy gap difference when the inter-detector separation is sufficiently large that renders the harvested entanglement to peak. Regarding the harvesting-achievable separation, we further find that the presence of an energy gap difference generally enlarges the harvesting-achievable separation range. Our results suggest that the non-identical detectors may be advantageous to extracting entanglement from vacuum in certain circumstances as compared to identical detectors.

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Fermi Problem with Artificial Atoms in Circuit QED

Cited by 36 publications

References 19 publications

Quantum signaling in cavity QED

Quantum signaling in cavity QED

Short-time quantum detection: Probing quantum fluctuations

Harvesting entanglement by non-identical detectors with different energy gaps

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