A dissipative quantum reservoir for microwave light using a mechanical oscillator

Abstract

Isolation of a system from its environment is often desirable, from precision measurements 1 to control of individual quantum systems; however, dissipation can also be a useful resource. Remarkably, engineered dissipation 2 enables the preparation of quantum states of atoms, ions or superconducting qubits 3-8 as well as their stabilization 9 . This is achieved by a suitably engineered coupling to a dissipative cold reservoir formed by electromagnetic modes. Similarly, in the field of cavity electro-and optomechanics 10 , the control over mechanical oscillators utilizes the inherently cold, dissipative nature of the electromagnetic degree of freedom. Breaking from this paradigm, recent theoretical work [11][12][13][14][15] has considered the opposite regime in which the dissipation of the mechanical oscillator dominates and provides a cold dissipative reservoir to an electromagnetic mode. Here we realize this reversed dissipation regime 13 in a microwave cavity optomechanical system 16 and realize a quasi-instantaneous, cold reservoir for microwave light. Coupling to this reservoir enables to manipulate the susceptibility of the microwave cavity, corresponding to dynamical backaction control of the microwave field. Additionally, we observe the onset of parametric instability, i.e. the stimulated emission of microwaves (masing) 17,18 . Equally important, the reservoir can function as a useful quantum resource. We evidence this by employing the engineered cold reservoir to implement a large gain (above 40 dB) phase preserving microwave amplifier that operates 0.87 quanta above the limit of added noise imposed by quantum mechanics (×2 above the device's quantum limit). Beyond offering the manipulation of microwave fields, such a dissipative cold reservoir, when coupled to multiple cavity modes, forms the basis of microwave entanglement schemes 11 , amplifiers with unlimited gain-bandwidth product 12 and the study of dissipative quantum phase transitions 19 . Moreover, combining such reservoir-mediated interaction with coherent dynamics allows for the realization of recently predicted non-reciprocal devices 15 . These devices could operate in the quantum regime when employing a cold reservoir as a quantum resource, thereby extending the available toolbox of quantum-limited microwave manipulation techniques [20][21][22][23][24] .Reservoir engineering defies the notion that dissipation is necessarily detrimental for the utility of a quantum system. In fact, if carefully constructed, dissipation can relax the system of interest to a desired target quantum state, e.g. an entangled state. This pioneering insight was first theoretically conceived and studied in the context of trapped ions 2 , experimentally first realized with trapped atomic ensembles 3 and later with trapped ions 4-6 . Moreover, reservoir engineering has recently also been realized in the context of circuit QED [7][8][9] . In these experiments the optical or microwave field provides a dissipative reservoir to the quantum systems. In cavity optomechanics 1...

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Efficient protocol for qubit initialization with a tunable environment

“…(8), we obtain the transition rates (10)- (12). For the eigenfrequency (38) and eigenstate (41) of the second excited state, we use the top signs when λ L+ (t) ≥ λ L− (t) and bottom signs when λ L+ (t) < λ L− (t). Note also that the eigenstates (37)- (39) …”

“…[25][26][27][28][29][30] Such engineering has already been used in generation of coherent superposition states, [31][32][33] in creation of entanglement, [34][35][36] and in simulations of open quantum systems. 37,38 In this paper, we focus on a ground-state initialization proposal, 39,40 where a superconducting qubit and a lowtemperature resistive bath are coupled indirectly through two resonators as shown in Fig. 1.…”

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