We present a theoretical analysis of a novel cavity electromechanical system where a mechanical resonator directly modulates the damping rate kappa of a driven electromagnetic cavity. We show that ...via a destructive interference of quantum noise, the driven cavity can effectively act like a zero-temperature bath irrespective of the ratio kappa/omega_{M}, where omega_{M} is the mechanical frequency. This scheme thus allows one to cool the mechanical resonator to its ground state without requiring the cavity to be in the so-called good cavity limit kappa << omega_{M}. The system described here could be implemented directly using setups similar to those used in recent experiments in cavity electromechanics.
Microwaves have widespread use in classical communication technologies, from long-distance broadcasts to short-distance signals within a computer chip. Like all forms of light, microwaves, even those ...guided by the wires of an integrated circuit, consist of discrete photons. To enable quantum communication between distant parts of a quantum computer, the signals must also be quantum, consisting of single photons, for example. However, conventional sources can generate only classical light, not single photons. One way to realize a single-photon source is to collect the fluorescence of a single atom. Early experiments measured the quantum nature of continuous radiation, and further advances allowed triggered sources of photons on demand. To allow efficient photon collection, emitters are typically placed inside optical or microwave cavities, but these sources are difficult to employ for quantum communication on wires within an integrated circuit. Here we demonstrate an on-chip, on-demand single-photon source, where the microwave photons are injected into a wire with high efficiency and spectral purity. This is accomplished in a circuit quantum electrodynamics architecture, with a microwave transmission line cavity that enhances the spontaneous emission of a single superconducting qubit. When the qubit spontaneously emits, the generated photon acts as a flying qubit, transmitting the quantum information across a chip. We perform tomography of both the qubit and the emitted photons, clearly showing that both the quantum phase and amplitude are transferred during the emission. Both the average power and voltage of the photon source are characterized to verify performance of the system. This single-photon source is an important addition to a rapidly growing toolbox for quantum optics on a chip.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
In a Rabi oscillation experiment with a superconducting qubit we show that a visibility in the qubit excited state population of more than 95% can be attained. We perform a dispersive measurement of ...the qubit state by coupling the qubit non-resonantly to a transmission line resonator and probing the resonator transmission spectrum. The measurement process is well characterized and quantitatively understood. In a measurement of Ramsey fringes, the qubit coherence time is larger than 500 ns.
We propose an experiment to create and verify entanglement between remote mechanical objects by use of an optomechanical interferometer. Two optical cavities, each coupled to a separate mechanical ...oscillator, are coherently driven such that the oscillators are laser cooled to the quantum regime. The entanglement is induced by optical measurement and comes about by combining the output from the two cavities to erase which-path information. It can be verified through measurements of degrees of second-order coherence of the optical output field. The experiment is feasible in the regime of weak optomechanical coupling. Realistic parameters for the membrane-in-the-middle geometry suggest entangled state lifetimes on the order of milliseconds.
Coupling isolated quantum systems through propagating photons is a central theme in quantum science1,2, with the potential for groundbreaking applications such as distributed, fault-tolerant quantum ...computing3–5. To date, photons have been used widely to realize high-fidelity remote entanglement6–12 and state transfer13–15 by compensating for inefficiency with conditioning, a fundamentally probabilistic strategy that places limits on the rate of communication. In contrast, here we experimentally realize a long-standing proposal for deterministic, direct quantum state transfer16. Using efficient, parametrically controlled emission and absorption of microwave photons, we show on-demand, high-fidelity state transfer and entanglement between two isolated superconducting cavity quantum memories. The transfer rate is faster than the rate of photon loss in either memory, an essential requirement for complex networks. By transferring states in a multiphoton encoding, we further show that the use of cavity memories and state-independent transfer creates the striking opportunity to deterministically mitigate transmission loss with quantum error correction. Our results establish a compelling approach for deterministic quantum communication across networks, and will enable modular scaling of superconducting quantum circuits.
We present measurements of single-qubit gate errors for a superconducting qubit. Results from quantum process tomography and randomized benchmarking are compared with gate errors obtained from a ...double pi pulse experiment. Randomized benchmarking reveals a minimum average gate error of 1.1+/-0.3% and a simple exponential dependence of fidelity on the number of gates. It shows that the limits on gate fidelity are primarily imposed by qubit decoherence, in agreement with theory.
Full manipulation of a quantum system requires controlled evolution generated by nonlinear interactions, which is coherent when the rate of nonlinearity is large compared with the rate of ...decoherence. As a result, engineered quantum systems typically rely on a bare nonlinearity much stronger than decoherence rates, and this hierarchy is usually assumed to be necessary. Here we challenge this assumption by demonstrating the universal control of a quantum system where the rate of bare nonlinear interaction is comparable to the fastest rate of decoherence. We introduce a noise-resilient protocol for the universal quantum control of a nearly harmonic oscillator that takes advantage of an in situ enhanced nonlinearity instead of harnessing a bare nonlinearity. Our experiment consists of a high-quality-factor microwave cavity with weak dispersive coupling to a superconducting qubit with much lower quality. By using strong drives to temporarily excite the oscillator, we realize an amplified three-wave-mixing interaction, achieving typical operation speeds over an order of magnitude faster than expected from the bare dispersive coupling. Our demonstrations include the preparation of a single-photon state with high fidelity, the generation of squeezed vacuum with large intracavity squeezing and measurement-free preparation of logical states for the binomial and Gottesman–Kitaev–Preskill quantum error-correcting codes.A noise-resilient protocol implemented in a cavity resonator coupled to a qubit demonstrates that large nonlinear couplings are not a necessary requirement for the fast universal control and state preparation of engineered quantum systems.
We analyze the Jaynes-Cummings model of quantum optics, in the strong-dispersive regime. In the bad-cavity limit and on time scales short compared to the atomic coherence time, the dynamics are those ...of a nonlinear oscillator. A steady-state nonperturbative semiclassical analysis exhibits a finite region of bistability delimited by a pair of critical points, unlike the usual dispersive bistability from a Kerr nonlinearity. This analysis explains our quantum trajectory simulations that show qualitative agreement with recent experiments from the field of circuit quantum electrodynamics.
Engineered quantum systems allow us to observe phenomena that are not easily accessible naturally. The LEGO®-like nature of superconducting circuits makes them particularly suited for building and ...coupling artificial atoms. Here, we introduce an artificial molecule, composed of two strongly coupled fluxonium atoms, which possesses a tunable magnetic moment. Using an applied external flux, one can tune the molecule between two regimes: one in which the ground-excited state manifold has a magnetic dipole moment and one in which the ground-excited state manifold has only a magnetic quadrupole moment. By varying the applied external flux, we find the coherence of the molecule to be limited by local flux noise. The ability to engineer and control artificial molecules paves the way for building more complex circuits for quantum simulation and protected qubits.
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