Quantum Measurement in Superconducting Circuits

Yuwei Ma, Wei‐Ting Wang, Jiajun Ma +6 more

Michael Hatridge

Kamal Sharma, Wade DeGottardi

Recent advances in superconducting circuit technology have made the fabrication of large, customizable circuits routine. This has led to applications beyond quantum information, including quantum simulation. A key challenge in this effort is the identification of the quantum states realized. Here, we propose a probe circuit capable of measuring many-body correlations in an analog quantum simulator superconducting circuit. This probe, which is specially designed for many-photon states, exploits the nonlinearity of the Josephson junction to measure two-point correlation functions of the superconducting phase operator. We demonstrate the capabilities of this design in the context of an LC-ladder with a quantum impurity. The proposed probe allows for the measurement of inherently quantum correlations, such as two-mode squeezing, and it has the potential to significantly expand the scope of analog quantum simulations using superconducting circuits.

P. M. Harrington

The interaction between a superconducting circuit and its environment can cause decoherence. However, interactions with an environment are necessary for quantum state preparation and measurement. Through the dynamics of open quantum systems, the environment is a resource to control and readout superconducting circuit states. I present an experimental result demonstrating qubit state stabilization from engineered dissipation with a microwave photonic crystal. In addition, I discuss the statistical arrow of time in the dynamics of continuous quantum measurement. These results demonstrate an interplay between open quantum system dynamics and statistics, which highlights the role of both dissipation and measurement for quantum control.

Sahel Ashhab

Victor T. Petrashov, K. G. Chua, K. M. Marshall +2 more

Using the extraordinary sensitivity of Andreev interferometers to the superconducting phase difference associated with currents, we measure the persistent current quantum states in superconducting loops interrupted by Josephson junctions. Straightforward electrical resistance measurements of the interferometers give a continuous readout of the states, allowing us to construct the energy spectrum of the quantum circuit. The probe is estimated to be more precise and faster than previous methods, and can measure the local phase difference in a wide range of superconducting circuits.