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Abstract

Effective quantum communication between remote quantum nodes requires high fidelity quantum state transfer and remote entanglement generation. Recent experiments have demonstrated that microwave photons, as well as phonons, can be used to couple superconducting qubits, with a fidelity limited primarily by loss in the communication channel. Adiabatic protocols can overcome channel loss by transferring quantum states without populating the lossy communication channel. In this thesis, we present a unique superconducting quantum communication system, comprising two superconducting qubits connected by a 0.73 m-long communication channel. We begin by discussing the operation of a qubit and a tunable coupler, the basic elements comprising our superconducting quantum node. Next, we describe a fast and large bandwidth variable coupler that allows us to introduce loss to the channel. Finally, we integrate all these elements together on-chip to form a tunably-dissipative quantum communication platform comprising two qubits coupled through a 0.73 m-long transmission line via a pair of electrically-tunable couplers. Significantly, we show that the integration of the variable coupler allows us to introduce large tunable loss to the channel, with which the single photon lifetime in the line can be controllably reduced from its intrinsic value by over two orders of magnitude. This enables exploration of different entanglement protocols in the presence of significant channel loss. When set for minimum loss in the channel, we demonstrate an adiabatic quantum state transfer protocol that achieves 99% transfer efficiency as well as the deterministic generation of entangled Bell states with a fidelity of 96%, all without populating the intervening communication channel, and competitive with a qubit-resonant mode-qubit relay method. We also explore the performance of the adiabatic protocol in the presence of significant channel loss, and show that the adiabatic protocol protects against loss in the channel, achieving higher state transfer and entanglement fidelities than the relay method.

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