Reduction of Decoherence in the Flux Qubit
Abstract
In collaboration with MIT-LL, UCB intensively studied superconducting flux qubits with two important modifications. The first is the addition of a capacitor across one or more of the junctions (C-shunt), thus ensuring that most of the electromagnetic energy is stored in this capacitor, potentially increasing T1. The second is a reduction of the critical current density of the junctions, reducing the sensitivity to flux noise and increasing T2. With a C-shunt across only the smallest junction, these modifications increased T1 to values as high as 30 us on degeneracy and 90 us away from degeneracy and T2 to values as high as 25 us. We have developed a new technique for phase matching the four-wave mixing process in the traveling wave parametric amplifier (TWPA) called resonant phase matching. By adding shunt resonators to the unit cell of the TWPA, the dispersion relation is modified near the resonance to correct the phase mismatch intrinsic to the nonlinear process. We have observed the effect of correcting the phase mismatch in a preliminary device, which achieved over 20 dB of gain with a full bandwidth of about 3 GHz. Noise measurements of the device show performance within a factor of 3 of the quantum limit.
Document Details
- Document Type
- Technical Report
- Publication Date
- Dec 08, 2014
- Accession Number
- ADA623734
Entities
People
- Irfan Siddiqi
- John Clarke
Organizations
- University of California, Berkeley