Relaxation of the Persistent Current Qubit by the Measurement Device

D. Nakada, J. C. Lee, Yi Yu

Terry P. Orlando, Lin Tian, Donald S. Crankshaw +4 more

Yang Yu, William D. Oliver, D. Nakada +3 more

We measured the energy relaxation time in a Nb superconducting persistent current qubit using a time-resolved fast measurement scheme. The energy relaxation time is longer than 10/spl mu/s, showing a strong potential of realizing quantum computation with Nb-based superconducting qubits.

Terrence D. Clark, Jason F. Ralph, M. J. Everitt +3 more

Lin Tian, Seth Lloyd, Terry P. Orlando

During measurement, information is transferred from the measured quantum system to the detector via their coupling. The same coupling that extracts information from the quantum system transmits noise from the detector's environment to the system as well. In this paper, we derive the limit to the measurement efficiency of a superconducting persistent-current qubit measured by a dc superconducting quantum interference device (SQUID) and calculate the noise transmitted to the qubit from the environment of the dc SQUID. The method, with simple linear circuitry correspondence, can be applied to calculate the noise transferred to a quantum system from the environment of an arbitrary external system that interacts with it. The relaxation and decoherence induced by this noise are also estimated.

Yang Yu, D. Nakada, Janice C. Lee +5 more

We measured the intrawell energy relaxation time tau(d) approximately 24 micros between macroscopic quantum levels in the double well potential of a Nb persistent-current qubit. Interwell population transitions were generated by irradiating the qubit with microwaves. Zero population in the initial well was then observed due to a multilevel decay process in which the initial population relaxed to lower energy levels during the driven transitions. The decoherence time, estimated from tau(d) within the spin-boson model, is about 20 micros for this configuration with a Nb superconducting qubit.