David Lucas

Abstract:

We describe and implement a method to restore the state of a single qubit, in principle perfectly, after it has partially collapsed. The method resembles the classical Hahn spin-echo, but works on a wider class of relaxation processes, in which the quantum state partially leaves the computational Hilbert space. It is not guaranteed to work every time, but successful outcomes are heralded. We demonstrate using a single trapped ion better performance from this recovery method than can be obtained employing projection and post-selection alone. The demonstration features a novel qubit implementation that permits both partial collapse and coherent manipulations with high fidelity.

Abstract:

Two cw single-mode violet (397 nm) diode lasers are locked to a single external-cavity master diode laser by optical injection locking. A double-pass 1.6 GHz acousto-optic modulator is used to provide a 3.2 GHz offset frequency between the two slave lasers. We achieve up to 20 mW usable output in each slave beam, with as little as 25 μW of injection power at room temperature. An optical heterodyne measurement of the beat note between the two slave beams gives a linewidth of ≤10 Hz at 3.2 GHz. We also estimate the free-running linewidth of the master laser to be approximately 3 MHz by optical heterodyning with a similar device. © 2013 Optical Society of America.