By coupling a macroscopic mechanical oscillator to two microwave cavities, we simultaneously prepare and monitor a nonclassical steady state of mechanical motion. In each cavity, correlated radiation pressure forces induced by two coherent drives engineer the coupling between the quadratures of light and motion. We, first, demonstrate the ability to perform a continuous quantum nondemolition measurement of a single mechanical quadrature at a rate that exceeds the mechanical decoherence rate, while avoiding measurement backaction by more than 13 dB. Second, we apply this measurement technique to independently verify the preparation of a squeezed state in the mechanical oscillator, resolving quadrature fluctuations 20% below the quantum noise.

Quantum fluctuations of the electromagnetic vacuum produce measurable physical effects such as Casimir forces and the Lamb shift [1]. Similarly, these fluctuations also impose an observable quantum limit to the lowest temperatures that can be reached with conventional laser cooling techniques [2,3]. As laser cooling experiments continue to bring massive mechanical systems to unprecedented temperatures [4,5], this quantum limit takes on increasingly greater practical importance in the laboratory [6]. Fortunately, vacuum fluctuations are not immutable, and can be "squeezed" through the generation of entangled photon pairs. Here we propose and experimentally demonstrate that squeezed light can be used to sideband cool the motion of a macroscopic mechanical object below the quantum limit. To do so, we first cool a microwave cavity optomechanical system with a coherent state of light to within 15% of this limit. We then cool by more than 2 dB below the quantum limit using a squeezed microwave field generated by a Josephson Parametric Amplifier (JPA). From heterodyne spectroscopy of the mechanical sidebands, we measure a minimum thermal occupancy of 0.19 ± 0.01 phonons. With this novel technique, even low frequency mechanical oscillators can in principle be cooled arbitrarily close to the motional ground state, enabling the exploration of quantum physics in larger, more massive systems.Rapid progress in the control and measurement of massive mechanical oscillators has enabled tests of fundamental physics, as well as applications in sensing and quantum information processing [7]. The noise performance of these experiments, however, is often limited by thermal motion of the mechanical mode. Although the most sophisticated refrigeration technologies can be sufficient for cooling high frequency mechanical structures to the ground state [8,9], observing quantum behavior in lower frequency mechanical systems requires other cooling methods. Recent efforts using active quantum feedback have been remarkably successful in preparing motional states with low entropies [10]. Thus far, however, only laser cooling techniques similar to those that revolutionized the coherent control of atomic systems [11,12] have yielded thermal occupancies below one quantum [4][5][6]. Nevertheless, vacuum fluctuations impose a lowest possible temperature that can be achieved using these techniques [2,3]. This limit is now being encountered in state of the art experiments involving macroscopic oscillators [6].The concept of sideband cooling relies on the removal of mechanical energy by scattering incident drive photons to higher frequencies. In general, however, this photon up-conversion (anti-Stokes) process competes with a downconversion (Stokes) process that adds energy to the mechanical system. In cavity optomechanics [7], a light-matter interaction arises due to a parametric modulation of an optical cavity's resonance frequency with a mechanical oscillator's position. When the cavity is driven at detuning ∆ below its resonance frequency, the dif...

We report the observation of efficient and low-noise frequency conversion between two microwave modes, mediated by the motion of a mechanical resonator subjected to radiation pressure. We achieve coherent conversion of more than 10 12 photons/s with a 95% efficiency and a 14 kHz bandwidth. With less than 10 −1 photons · s −1 · Hz −1 of added noise, this optomechanical frequency converter is suitable for quantum state transduction. We show the ability to operate this converter as a tunable beam splitter, with direct applications for photon routing and communication through complex quantum networks.The interaction between electromagnetic radiation and other quantum systems is ubiquitous in quantum information processing and quantum measurement. Photons can be used to control and measure the quantum state of atoms 1 , ions 2 , solid state spins 3 , superconducting qubits 4 , or the motion of macroscopic objects 5 . Hence, light fields are ideally suited for coherently connecting nodes in a quantum networks 6 . As in a classical communication network, the ability to shuttle information between different frequency channels is critical in a quantum network. In particular, a frequency converter can be used to route information through complex node architectures or distribute entanglement between systems of vastly different nature and frequency.While frequency conversion naturally arises in any nonlinear system, a frequency converter ideally suited for quantum information processing has to perform a unitary conversion, as signal loss or gain corrupts the quantum signal 7 . In the optical domain, using media such as nonlinear crystals 8 and optical fibers, it remains challenging to achieve high system efficiency while avoiding or removing unwanted noise generation processes 9 . In the microwave domain, the development of superconducting mixing elements based on Josephson junctions has enabled near-ideal frequency conversion between microwave signals with appreciable bandwidth, but with very low power handling capability 10,11 . Additionally, these systems are intrinsically limited to signals in the microwave domain because superconductivity is incompatible with optical light.Recently, experimental breakthroughs in cavity optomechanical systems have enabled the frequency conversion of optical or microwave photons into mechanical phonons 12-14 . By coupling a single mechanical element to two different cavities, one can achieve frequency conversion between the two light fields [15][16][17][18][19] . Because of the universal nature of the optomechanical coupling, conversion between microwave and optical frequencies can be achieved [20][21][22] . However, current implementations have suffered from a low conversion efficiency and from a large added noise due to the residual Brownian motion of the mechanical resonator. Here we report on the observation of parametric frequency conversion between two microwave modes mediated by the motion of a mechanical resonator. We achieve a conversion rate between microwave photons and mechan...

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