Strong Single-Photon Coupling in Superconducting Quantum Magnetomechanics

Abstract

We show that the inductive coupling between the quantum mechanical motion of a superconducting microcantilever and a flux-dependent microwave quantum circuit can attain the strong singlephoton nanomechanical coupling regime with feasible experimental parameters. We propose to use a superconducting strip, which is in the Meissner state, at the tip of a cantilever. A pick-up coil collects the flux generated by the sheet currents induced by an external quadrupole magnetic field centered at the strip location. The position-dependent magnetic response of the superconducting strip, enhanced by both diamagnetism and demagnetizing effects, leads to a strong magnetomechanical coupling to quantum circuits.In quantum nanomechanics, the strength of the radiation-pressure interaction between a single electromagnetic mode of frequency ω and a micromechanical mode of frequency Ω and effective mass M is denoted by g 0 , the so-called single-photon coupling rate [1]. This is the cavity frequency shift due to a zero-point motion displacement of the mechanical oscillator, given by1/2 , namely g 0 = z zp ∂ω/∂z| z=0 . The singlephoton coupling, being non-linear, could be exploited to observe non-Gaussian physics in micromechanical oscillators [2][3][4][5][6][7], a goal that would represent a milestone in the field [1]. However this is today experimentally very challenging. The mechanical mode (electromagnetic mode) suffers decoherence with a rate Γ (κ) whose origin depends on the particular experimental implementation. To fully exploit the non-Gaussian character of the single-photon nanomechanical coupling one would like to operate in the strong-coupling regime g 0 Γ, κ as well as in the resolved sideband regime Ω/κ 1. The latter is required to sideband cool the mechanical mode into the ground state [8][9][10]. While g 0 /Γ 1 and Ω/κ 1 has been achieved simultaneously in several experiments [1], the so-called single-photon strong coupling regime g 0 /κ 1 is much more challenging. Indeed, according to [1], the highest values of g 0 /κ obtained so far with solid mesoscopic objects are ∼ 10 −3 [11,12] (with cold gases one achieves g 0 /κ ∼ 1 [13, 14] but not in the resolved sideband regime).In this Letter we propose a microwave optomechanical scenario, see Fig. 1, where we show that the strong single-photon regime g 0 /κ 1 can be achieved in the resolved sideband regime with feasible experimental parameters. Contrary to most of the current experiments in microwave optomechanics [1,12], where the optomechanical coupling is implemented capacitively, here we motivate to use an inductive coupling to a flux-dependent quantum circuit as a way to obtain three orders of magnitude stronger couplings. Such a strong quantum magnetomechanical (MM) coupling is achieved via the magnetic response of a superconducting (SC) strip in an inhomogenous external field that is strengthened by the large FIG. 1: (Color online) Schematic illustration of the proposal (not to scale). A superconducting strip of length L and widthw is deposited on the tip of the c...

Optomechanical measurement of a millimeter-sized mechanical oscillator approaching the quantum ground state

“…As already mentioned, systems described by equation (1) can be physically built from very different ingredients. In qubit-mediated cavity optomechanics [25][26][27][28]34], see figure 1(b), the qubit can drastically enhance the intrinsically small radiation-pressure coupling g 0 between the mechanics and an microwave cavity. This is because a large linear coupling, created by applying a dc bias to the qubit, becomes converted into an effective parametric coupling as reviewed in the following.…”

Preparation of a nonlinear coherent state of the mechanical resonator in an optomechanical microcavity

“…This challenging idea has inspired emerging attentions from experimental field. The nonlinearity of the phonon mode of the MR originating from the strong coupling between the microcavity and the MR has been discussed based on capacitive [73] or magnetic [74] coupling in the microwave-regime optomechanical devices. By enhancing the effect of a single-photon in the optical cavity, the strong-coupling regime is reached with the auxiliary of the squeezing of a cavity mode [4].…”

Dual-lens beam compression for optical coupling in superconducting nanowire single-photon detectors

“…Superconducting nanowire single-photon detectors (SNSPDs) have shown promise for applications in quantum communication and computation [1][2][3][4][5][6][7][8][9]. In particular, they have been developed because they offer the advantages of a low dark count rate (DCR), a short time jitter, broadband response, and a high repetition rate [10][11][12][13][14].…”