All-Optical Hadamard Gate: Direct Implementation of a Quantum Information Primitive

Abstract

The ultrafast optical spin control techniques described in Chap. 3 were derived under the assumption of the pulses being short compared to the Larmor precession frequency. In practice, however, picosecond-timescale pulses are used, combined with Larmor precession periods of several tens of picoseconds [1, 2]. While lowering the magnetic field and increasing the Larmor precession period would render the picosecond pulses (relatively) ‘shorter’, this would come at the expense of the speed of elementary quantum gates (the Larmor precession acts as one of the fundamental 1-qubit gates). In addition, decreasing the magnetic field lowers the spin readout fidelity, as the filtering of the optical pumping laser becomes more troublesome – we refer to Sect. 3.2.1 and Appendix A.1.1.