A Novel Superconducting Device to Isolate, Entangle and Read Out Flux Qubits
Abstract
Experiments are described in which the quantum states of two flux qubits were read out by a dc SQUID (Superconducting QUantum Interference Device). Observations of the linewidths of microwave-induced peaks. Ramsey fringes and flux echoes on a single qubit yielded values of the decoherence times T(sub 2)', T(sub 2)* and T(sub 2). respectively. Within the experimental errors, the values satisfied the prediction 1/T(sub 2)* =1/T(sub 2)' + 1/T(sub 2). Spectroscopic measurements on two qubits revealed energy gaps at their degeneracy points matched to within plus or minus 1%: 8.88 plus or minus 0.01 GHz and 8.9 plus or minus 0.01 GHz, respectively. Detailed measurements were made of the entangled states of the qubits in two regimes: at the double degeneracy point (both qubits biased at a half-flux quantum phi(sub 0)/2). and at flux values away from phi(sub 0)/2 at which two qubit frequencies coincided ("intersecting anticrossing"). The energy levels were determined from microwave transitions from the ground state| 0 > to the first and second excited states | 1 > and | 2 >. At the double degeneracy point, a repulsion of the two-energy levels was observed while at the intersecting anticrossing. an avoided crossing was observed. The measured energies were in excellent agreement with calculations with no fitted parameters. Furthermore, the energy splitting at the intersecting anticrossing could be controlled by means of a current bias pulse in the readout SQUID, as predicted theoretically.
Document Details
- Document Type
- Technical Report
- Publication Date
- Feb 21, 2006
- Accession Number
- ADA449194
Entities
People
- John Clarke
Organizations
- University of California, Berkeley