Engineering Exotic Baths for Superconducting Quantum Circuits Using Parametric DrivesMucci, Maria (2024) Engineering Exotic Baths for Superconducting Quantum Circuits Using Parametric Drives. Doctoral Dissertation, University of Pittsburgh. (Unpublished)
AbstractQuantum bits, or qubits, must be coupled to their environmental bath in order for us to measure and manipulate their delicate quantum states. This qubit-bath interaction introduces irreversible decay in superconducting circuits where information is lost to dissipations. While loss and decay are inevitable, loss need not be our enemy. The work described in this thesis focuses on engineering losses and effective baths for quantum systems to, for instance, gain in-situ control of the effective temperature\slash populations and relaxation rates of a multi-level transmon qubit. We create fully engineered baths where the user can modulate the couplings between qubits and their environment, determining how energy is gained and lost by the qubit through a designed loss channel. We achieve an engineered qubit-reservoir exchange by dispersively coupling a single transmon qubit to a SNAIL mode. The SNAIL has two functions: first to be the source of three- (and sometimes four-) wave mixing that allows us to drive parametric operations to create and exchange photons among the qubit and SNAIL modes at a rate of our choosing, and second to be a source of loss that converts these coherent processes to controlled heating and cooling of the transmon. This thesis will highlight two experimental use cases for such a multimode system. First, a fully controllable quantum bath where we can push the qubit towards states with positive, negative, and infinite temperature, and even make `unnatural’ relaxation states such as a transmon that relaxes equally from |e> to |g> and |f>. These transmons may have applications in problems like cavity arrays and quantum simulators because the computers that simulate quantum behavior should themselves be quantum mechanical in nature. Second, we use parametric transmon heating to realize a single-atom micro-maser as a very narrow cryogenic light source. We generate a maser that is emits a narrow bandwidth of high amplitude light with indirect, far-detuned microwave drives that excite our transmon artificial atom. This is an ideal platform for studying quantum optics in a microwave circuit setting, for instance realizing a recent proposal to build a maser far narrower than the Schawlow-Townes limit. Share
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