Engineering Quantum Interactions in Micromechanical Circuits
John Teufel, U.S. National Institute of Standards and Technology
While the rules of quantum mechanics routinely dictate the interaction of particles at the microscopic scale, it is only recently that the behavior of engineered mechanical systems deviates from a classical description. One successful approach for exploring the quantum nature of mechanical resonators has been to take advantage of optomechanical interactions in which the radiation pressure forces of light both control and measure the motion . In this way, the mature tools of quantum optics may now be exploited to investigate quantum states of motion. In our work, the “light” is not at visible, but microwave, frequencies, where superconducting devices can be used to create highly non-classical photon states. Using the latest nanofabrication techniques, we engineer superconducting electro- mechanical circuits in which microwave photons strongly interact with the motion of micromechanical resonators . When operated at cryogenic temperatures, the resulting hybrid quantum systems allow us unprecedented tools for combining electrical, mechanical and photonic degrees of freedom.
I will discuss our current experimental research at NIST in which these engineered macroscopic circuits exhibit demonstrably quan- tum behavior. By simply choosing the exact frequency of the applied microwave fields, we can select the interaction Hamiltonian of the system to perform either a “beam-splitter” or “dual-mode squeezing” operation between the electromagnetic and mechanical resonators. These two operations correspond to the coherent transfer or amplification of the motional states, respectively. When combined with a superconducting quantum bit (a qubit) co-fabricated with the electromechanical circuit, we experimentally verify a protocol that converts the quantum vacuum fluctuations of the micromechanical resonator into real microwave photons that can be measured and quantified . This demonstration is a first step toward engineering arbitrary quantum states of massive mechanical structures and literally putting an object in two places at once.
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 F. Lecocq et al. “‘Resolving the vacuum fluctuations of an optomechanical system using an artificial atom,” to appear in Nature Physics, (2015).