Superconducting qubit as a probe of squeezing in a nonlinear resonator

Boissonneault, Maxime; Doherty, Andrew C.; Ong, Florian; Bertet, Patrice; Vion, Denis; Estève, D.; Blais, Alexandre

doi:10.1103/physreva.89.022324

Cited by 11 publications

(15 citation statements)

References 47 publications

(106 reference statements)

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“…Generation and measurement of squeezing has been the subject of much recent research in the field of circuit QED [59][60][61][62]. When U = 0, it is known that the maximum squeezing the can be achieved is a factor of 2, reducing the fluctuations in one field quadrature to 50% of those of the vacuum state [1].…”

Section: Generation Of Squeezingmentioning

confidence: 99%

Applications of the Fokker-Planck equation in circuit quantum electrodynamics

Elliott

Ginossar

2016

Phys. Rev. A

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We study exact solutions of the steady state behaviour of several non-linear open quantum systems which can be applied to the field of circuit quantum electrodynamics. Using Fokker-Planck equations in the generalised P -representation we investigate the analytical solutions of two fundamental models. First, we solve for the steady-state response of a linear cavity that is coupled to an approximate transmon qubit and use this solution to study both the weak and strong driving regimes, using analytical expressions for the moments of both cavity and transmon fields, along with the Husimi Q-function for the transmon. Second, we revisit exact solutions of quantum Duffing oscillator which is driven both coherently and parametrically while also experiencing decoherence by the loss of single and pairs of photons. We use this solution to discuss both stabilisation of Schrödinger cat states and the generation of squeezed states in parametric amplifiers, in addition to studying the Q-functions of the different phases of the quantum system. The field of superconducting circuits, with its strong nonlinearities and couplings, has provided access to new parameter regimes in which returning to these exact quantum optics methods can provide valuable insights.

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Section: Generation Of Squeezingmentioning

confidence: 99%

Applications of the Fokker-Planck equation in circuit quantum electrodynamics

Elliott

Ginossar

2016

Phys. Rev. A

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“…The nonlinear cavity response [22][23][24][25][26][27][28][29][30][31][32][33][34][35][36] is measured as a function of the magnetic flux that is applied to the qubit. At weak driving and when the ratio between the qubit frequency and the cavity fundamental mode frequency is tuned close to the value ω a /ω c = 1 the common Jaynes-Cummings resonance, which henceforth is referred to as the primary resonance, is observed.…”

mentioning

confidence: 99%

Superharmonic resonances in a strongly coupled cavity-atom system

Buks¹,

Deng²,

Orgazzi³

et al. 2016

Phys. Rev. A

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We study a system consisting of a superconducting flux qubit strongly coupled to a microwave cavity. The fundamental cavity mode is externally driven and the response is investigated in the weak nonlinear regime. We find that near the crossing point, at which the resonance frequencies of the cavity mode and qubit coincide, the sign of the Kerr coefficient changes, and consequently the type of nonlinear response changes from softening to hardening. Furthermore, the cavity response exhibits superharmonic resonances when the ratio between the qubit frequency and the cavity fundamental mode frequency is tuned close to an integer value. The nonlinear response is characterized by the method of intermodulation and both signal and idler gains are measured. Cavity quantum electrodynamics (CQED) [1] is the study of the interaction between photons confined in a cavity and atoms (natural or artificial). The interaction is commonly described by the Rabi or Jaynes-Cummings Hamiltonians [2], and it has been the subject of numerous theoretical and experimental investigations. An on-chip CQED system can be realized by integrating a Josephson qubit [3][4][5] (playing the role of an artificial atom) with a superconducting microwave resonator (cavity) [6][7][8]. Superconducting CQED systems have generated a fast growing interest due to the possibility to reach the strong [7] and ultra-strong [9, 10] coupling regimes, and due to potential applications in quantum information processing [4,[11][12][13].In this study we investigate the driven dynamics of a strongly interacting system composed of a superconducting flux qubit [15,16] and a coplanar waveguide (CPW) microwave cavity [9,14,[17][18][19][20][21]. The nonlinear cavity response [22][23][24][25][26][27][28][29][30][31][32][33][34][35][36] is measured as a function of the magnetic flux that is applied to the qubit. At weak driving and when the ratio between the qubit frequency and the cavity fundamental mode frequency is tuned close to the value ω a /ω c = 1 the common Jaynes-Cummings resonance, which henceforth is referred to as the primary resonance, is observed. With stronger driving, however, and when the ratio ω a /ω c is tuned close to integer values larger than unity, superharmonic resonances appear in the measured response. Intermodulation (IMD) measurements are employed to characterize the nonlinear response [37][38][39]. The results are compared with the predictions of a theoretical model, which is based on linearization of the equations of motion that govern the dynamics of the CQED system under study.

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“…Here, however, on-chip amplification drives a second, parasitic measurement process in whichσ z information is encoded in other statistical moments of the output field. This dephasing mechanism is predicted to be independent of the mean field in the resonator, making it distinct from effects in resonantly current-pumped systems [25][26][27][28][29][30]. A rough heuristic model describes the parasitic measurement in two steps: the phase-sensitive on-chip gain squeezes the microwave vacuum noise, and the resultant output squeezed state is rotated in phase by the dispersive interaction, encodingσ z information in the covariance of the outputfield quadratures.…”

Section: Measurement Backaction With On-chip Gainmentioning

confidence: 99%

High-Efficiency Measurement of an Artificial Atom Embedded in a Parametric Amplifier

et al. 2019

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A crucial limit to measurement efficiencies of superconducting circuits comes from losses involved when coupling to an external quantum amplifier. Here, we realize a device circumventing this problem by directly embedding a two-level artificial atom, comprised of a transmon qubit, within a flux-pumped Josephson parametric amplifier. Surprisingly, this configuration is able to enhance dispersive measurement without exposing the qubit to appreciable excess backaction. This is accomplished by engineering the circuit to permit high-power operation that reduces information loss to unmonitored channels associated with the amplification and squeezing of quantum noise. By mitigating the effects of off-chip losses downstream, the on-chip gain of this device produces end-toend measurement efficiencies of up to 80%. Our theoretical model accurately describes the observed interplay of gain and measurement backaction, and delineates the parameter space for future improvement. The device is compatible with standard fabrication and measurement techniques, and thus provides a route for definitive investigations of fundamental quantum effects and quantum control protocols. arXiv:1806.05276v1 [quant-ph]

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Superconducting qubit as a probe of squeezing in a nonlinear resonator

Cited by 11 publications

References 47 publications

Applications of the Fokker-Planck equation in circuit quantum electrodynamics

Applications of the Fokker-Planck equation in circuit quantum electrodynamics

Superharmonic resonances in a strongly coupled cavity-atom system

High-Efficiency Measurement of an Artificial Atom Embedded in a Parametric Amplifier

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