Dynamics of a Phase Qubit-Resonator System: Requirements for Fast Nondemolition Readout of a Phase Qubit

Abstract

We examine the non-stationary evolution of a coupled qubittransmission line-resonator system coupled to an external drive and the resonator environment. By solving the equation for a non-stationary resonator field, we determined the requirements for a single-shot nondestructive dispersive measurement of the phase qubit state. Reliable isolation of the qubit from the "electromagnetic environment" is necessary for a dispersive readout and can be achieved if the whole system interacts with the external fields only through the resonator that is * Corresponding author: gpb@lanl.gov weakly coupled to the qubit. A set of inequalities involving resonatorqubit detuning and coupling parameter, the resonator leakage and the measurement time, together with the requirement of multi-photon outgoing flux is derived. It is shown, in particular, that a decrease of the measurement time requires an increase of the resonator leakage. This increase results in reducing the quality factor and decreasing the resolution of the resonator eigenfrequencies corresponding to different qubit states. The consistent character of the derived inequalities for two sets of experimental parameters is discussed.The obtained results will be useful for optimal design of experimental setups, parameters, and measurement protocols.

Optimizing Qubit Performance through Smoothing Techniques

“…The variations observed in the Hamiltonian spectra emphasize the sensitivity of the quantum system to frequency differences and offer valuable insights into the intricate dynamics of qubit-resonator interactions One crucial factor affecting the quality of spectroscopy data is the variation in parameters, such as the signal power on the qubit and resonator 22 . When the resonance frequencies of the qubit and resonator are close 23 , the more sensitive the qubit is to the signal (i.e., it requires less power [in dBm] to be detected/observed as a line in the spectroscopy). Experimenters face the challenging task of optimizing these parameters optimal results.…”

Non-demolition dispersive measurement of a superconducting qubit with a microstrip SQUID amplifier

“…This requires reduction of the size of the MSA input coil, which diminishes its coupling with the SQUID [11]. One could raise the input voltage of the MSA increasing the number of photons in MR but this causes a back reaction of the MR on the QL, and the dispersive measurement becomes a demolition measurement [13][14][15].…”