Princeton University

School of Engineering & Applied Science

Tunable Coupling and Its Applications in Circuit Quantum Electrodynamics

Gengyan Zhang
Prof. Houck
Engineering Quadrangle J401
Wednesday, May 16, 2018 - 10:30am to 12:00pm

Circuit quantum electrodynamics (cQED) is a promising experimental platform for quantum computation and quantum simulation. It uses superconducting circuit elements as building blocks for quantum information processing. We explore the ability to tune the coupling rate between circuit elements in cQED devices, and present two experiments that demonstrate the application of tunable coupling for better device performance. The tunability originates from the basic principles of quantum superposition and interference, and unwanted interactions can be suppressed when the coupling rates are engineered to destructively interfere with each other.
The first experiment realizes a novel device to improve the robustness of quantum information encoded in a quantum bit (qubit) against noise. It is a well known difficulty in quantum information processing to prevent noise in the environment from disturbing the quantum state of a qubit. We design and implement a superconducting qubit that can decouple itself from a noisy environment, and demonstrate the robust preparation, manipulation and measurement of the qubit in the presence of noise. This approach provides a promising element for the storage and processing of quantum information.
The second experiment extends to a multi-qubit system where crosstalk between qubits causes error in quantum gates. We develop a two-qubit device and suppress crosstalk by tuning the ZZ coupling rate between the qubits to near zero. The tunable dispersive coupling can also be parametrically modulated to implement a two-qubit entangling gate in the low crosstalk regime. This device has the potential of reducing error rate in cQED systems as the number of qubits scales up.