Development of Superconductor Circuits for Readout of Quantum Nanomechanical Resonators

The LaHaye lab (Syracuse University) has been utilizing the nanofabrication facilities at Cornell NanoScale Science and Technology Facility (CNF) to develop a new hybrid quantum system that involves the integration of nanomechanical systems with state-of-the-art technology from the field of superconducting quantum computing. In recent years, the LaHaye group began studying the complex behavior of this quantum electromechanical system, and is currently following up on these initial experiments with plans to optimize the system to serve as a platform for generating and studying non-classical states of motion at the nanoscale [1]. With further development, this system could have applications for quantum information processing, quantum thermodynamics, and the study of fundamental topics that are of central interest to emerging quantum-enabled technologies. Summary of Research: Hybrid quantum systems — systems consisting of multiple elements with distinct functionality that each behave quantum mechanically — are being developed for a range of quantum­enabled applications, including quantum information processing and quantum­limited sensing [2,3]. They also offer prospects for studying fundamental topics of direct relevance to these applications, such as quantum decoherence [4­6] and quantum fluctuation theorems [7,8]. The LaHaye group is developing a particular hybrid quantum system that could serve as a versatile platform for pursuing many of these directions (Figures 1 and 2). The system is composed of three devices: a superconducting quantum bit (qubit) [9], superconducting microwave resonator (SMR) [10], and flexural nanomechanical resonator (nanoresonator) [1]. These components are integrated on a silicon wafer and can be coupled together and probed via the application of DC and microwave signals. This architecture is analogous to that of systems used in cavity and circuit quantum electrodynamics, where atoms and artificial atoms — such as superconducting quantum bits — are used for studying the quantum properties of light [10]. It is thus expected that this electromechanical analog should enable exploration of quantum behavior of the nanoresonator [5,6,11]. For instance, it should allow for the creation and measurement of nanoresonator superposition states, which would enable experiments to probe decoherence with the nanoresonator [5,6] and also be an important step toward utilizing the nanoresonator as quantum coherent circuit element (such as quantum switch [12], transducer [13], or memory device [14]). In the first series of experiments pursued by the LaHaye group in 2015 and 2016, the qubit served as an element for measuring the nanoresonator; similarly, the SMR functioned to control and probe the state of the qubit. In the last year, the LaHaye group published results that characterized the interactions between the components of this tripartite system at milli­Kelvin temperatures — temperatures where each element resides near its quantum ground state [1]. These measurements were performed in the weak coupling limit between the nanoresonator and qubit, where the strength of