Superconducting thin-film metamaterial resonators can provide a dense microwave mode spectrum with potential applications in quantum information science. We report on the fabricationand low-temperature measurement of metamaterial transmission-line resonators patterned from Al thin films. We also describe multiple approaches for numerical simulations of the microwave properties of these structures, along with comparisons with the measured transmission spectra. The ability to predict the mode spectrum based on the chip layout provides a path towards future designs integrating metamaterial resonators with superconducting qubits.
Superconducting systems have a long history of use in experiments that push the frontiers of mechanical sensing. This includes both applied and fundamental research, which at presentday ranges from quantum computing research and efforts to explore Planck-scale physics to fundamental studies on the nature of motion and the quantum limits on our ability to measure it. In this paper, we first provide a short history of the role of superconducting circuitry and devices in mechanical sensing, focusing primarily on efforts in the last decade to push the study of quantum mechanics to include motion on the scale of human-made structures. This background sets the stage for the remainder of the paper, which focuses on the development of quantum electromechanical systems (QEMS) that incorporate superconducting quantum bits (qubits), superconducting transmission line resonators and flexural nanomechanical elements. In addition to providing the motivation and relevant background on the physical behavior of these systems, we discuss our recent efforts to develop a particular type of QEMS that is based upon the Cooper-pair box (CPB) and superconducting coplanar waveguide (CPW) cavities, a system which has the potential to serve as a testbed for studying the quantum properties of motion in engineered systems.
We present the design of a reflective stop-band filter based on quasi-lumped elements that can be utilized to introduce large dc and low-frequency voltage biases into a low-loss superconductingcoplanar waveguide (CPW) cavity. Transmission measurements of the filter are seen to be in good agreement with simulations and demonstrate insertion losses greater than 20dB in the range of 3to10GHz. Moreover, transmission measurements of the CPW’s fundamental mode demonstrate that loaded quality factors exceeding 105 can be achieved with this design for dc voltages as large as 20V and for the cavity operated in the single-photon regime. This makes the design suitable for use in a number of applications including qubit-coupled mechanical systems and circuit QED.
Over the past several decades, a rich series of experiments has repeatedly verified the quantum nature of superconducting devices, leading some of these systems to be regarded as artificialatoms. In addition to their application in quantum information processing, these `atoms‘ provide a test bed for studying quantum mechanics in macroscopic limits. Regarding the last point, we present here a feasible protocol for directly testing time reversal symmetry in a superconducting artificial atom. Time reversal symmetry is a fundamental property of quantum mechanics and is expected to hold if the dynamics of the artificial atom strictly follow the Schroedinger equation. However, this property has yet to be tested in any macroscopic quantum system. The test we propose is based on the verification of the microreversibility principle, providing a viable approach to verify quantum work fluctuation theorems – an outstanding challenge in quantum statistical mechanics. For this, we outline a procedure that utilizes the microreversibility test in conjunction with numerical emulations of Gibbs ensembles to verify these theorems over a large temperature range.