Coherent Oscillations in a SQUID Qubit Manipulated without Microwaves

speaker: Alexey Ustinov (University of Karlsruhe)

abstract: We report the experimental demonstration of tunable coherent oscillations measured in a superconducting flux qubit without using microwave signals. The studied qubit is a double-SQUID resembling on rf-SQUID with tunable critical current. In a double well situation the two eigenvectors that define the computational base of our qubit are localized in the two local minima and physically correspond to a clockwise and anticlockwise circulating current. The whole sequence of preparation, manipulation and readout is possible by manipulating the potential energy profile via two external bias fluxes that control the height of the barrier between the minima and the potential symmetry, and is realized with nanosecond-long pulses. Preparation and readout are performed in a double well situation while coherent evolution is carried out with the potential profile transformed to a single well. Due to the large energy level separation during coherent evolution the system oscillates with frequencies ranging from 6 to 30 GHz. The reported approach seems particularly promising for the realization of circuits with many qubits, and it appears to be well suited for integration with RSFQ control electronics. The benefits of the reported system are the possibility of in situ tuning the frequency of oscillations and their insensitivity to small changes in the potential symmetry. The high frequency of oscillations allows for very fast qubit gate operations, and the large energy gap between the qubit states during coherent evolution protects the system from thermal activation to upper energy states. Moreover, the oscillation frequency depends only weakly on the control pulse amplitude, in contrast to the exponential sensitivity of the oscillations in a double well potential, which makes the qubit manipulation more reliable.

timetable:
Fri 5 Dec, 9:00 - 9:30, Sala Stemmi
<< Go back