The ability to engineer and manipulate different varieties of quantum mechanical objects allows us to take advantage of their unique properties and create useful hybrid technologies 1 .Thus far, complex quantum states and exquisite quantum control have been demonstrated in systems ranging from trapped ions 2, 3 and solid state qubits 4,5 to superconducting microwave resonators 6,7 . Recently, there have been many efforts 8,9 to extend these demonstrations to the motion of complex, macroscopic objects. These mechanical objects have important practical applications in the fields of quantum information and metrology as quantum memories or transducers for measuring and connecting different types of quantum systems. In pursuit of such macroscopic quantum phenomena, mechanical oscillators have been interfaced with quantum devices such as optical cavities and superconducting circuits [10][11][12] . In particular, there have been a few experiments that couple motion to nonlinear quantum objects [13][14][15] such as superconducting qubits. Importantly, this opens up the possibility of creating, storing, and manipulating non-Gaussian quantum states in mechanical degrees of freedom. However, before sophisticated quantum control of mechanical motion can be achieved, we must overcome the challenge of realizing systems with long coherence times while maintaining a 1 arXiv:1703.00342v1 [quant-ph] 1 Mar 2017 sufficient interaction strength. These systems should be implemented in a simple and robust manner that allows for increasing complexity and scalability in the future. Here we experimentally demonstrate a high frequency bulk acoustic wave resonator that is strongly coupled to a superconducting qubit using piezoelectric transduction. In contrast to previous experiments with qubit-mechanical systems [13][14][15] , our device requires only simple fabrication methods, extends coherence times to many microseconds, and provides controllable access to a multitude of phonon modes. We use this system to demonstrate basic quantum operations on the coupled qubit-phonon system. Straightforward improvements to the current device will allow for advanced protocols analogous to what has been shown in optical and microwave resonators, resulting in a novel resource for implementing hybrid quantum technologies.Measuring and controlling the motion of massive objects in the quantum regime is of great interest for both technological applications and for furthering our understanding of quantum mechanics in complex systems. In some respects, the physics of phonons inside a crystal is similar to that of photons inside an electromagnetic resonator, which are routinely treated as quantum mechanical objects. However, such mechanical excitations involve the collective motion of a large number of atoms in the complex environment of a macroscopic object. Nevertheless, there has only been one demonstration of a nonlinear electromechanical system in the strong coupling limit 13 . The outstanding question is how to simultaneously achieve coherences 3 and c...

Quantum states of mechanical motion can be important resources for quantum information, metrology, and studies of fundamental physics. Recent demonstrations of superconducting qubits coupled to acoustic resonators have opened up the possibility of performing quantum operations on macroscopic motional modes 1-3 , which can act as long-lived quantum memories or transducers. In addition, they can potentially be used to test for novel decoherence mechanisms in macroscopic objects and other modifications to standard quantum theory 4, 5 .Many of these applications call for the ability to create and characterize complex quantum states, putting demanding requirements on the speed of quantum operations and the coherence of the mechanical mode. In this work, we demonstrate the controlled generation of multi-phonon Fock states in a macroscopic bulk-acoustic wave resonator. We also perform Wigner tomography and state reconstruction to highlight the quantum nature of the prepared states 6 . These demonstrations are made possible by the long coherence times of our acoustic resonator and our ability to selectively couple to individual phonon modes. Our work shows that circuit quantum acousto-dynamics (circuit QAD) 7 enables sophisticated 1 arXiv:1804.07426v2 [quant-ph]

Photonic-integrated circuits have emerged as a scalable platform for complex quantum systems. A central goal is to integrate single-photon detectors to reduce optical losses, latency and wiring complexity associated with off-chip detectors. Superconducting nanowire single-photon detectors (SNSPDs) are particularly attractive because of high detection efficiency, sub-50-ps jitter and nanosecond-scale reset time. However, while single detectors have been incorporated into individual waveguides, the system detection efficiency of multiple SNSPDs in one photonic circuit—required for scalable quantum photonic circuits—has been limited to <0.2%. Here we introduce a micrometer-scale flip-chip process that enables scalable integration of SNSPDs on a range of photonic circuits. Ten low-jitter detectors are integrated on one circuit with 100% device yield. With an average system detection efficiency beyond 10%, and estimated on-chip detection efficiency of 14–52% for four detectors operated simultaneously, we demonstrate, to the best of our knowledge, the first on-chip photon correlation measurements of non-classical light.