Magnetic flux quanta in YBa2Cu3O7-delta thin-film loops controlled by femtosecond optical pulses

The optical control of magnetic flux in superconducting thin-film loops is studied by terahertz radiation imaging. The magnetic flux quanta phi are ge nerated in the loop by illuminating it with femtosecond optical pulses unde r the bias current I-B. The optically generated phi are semiqualitatively e valuated by estimating the amount of the persistent supercurrent circulatin g along the loop. The threshold and hysteretic characteristics are found in the phi -I-B curves, which strongly depend on optical excitation condition s such as laser power and bias current.