Fig. 1: Pulse cancellation.
From: Quantum efficiency, purity and stability of a tunable, narrowband microwave single-photon source
a Schematic for generating single photons using pulse cancellation. A flux-tunable transmon-type superconducting qubit (artificial atom) capacitively coupled to the end of an open transmission line with a −20 dB directional coupler connected to the transmission line. Cs and Cc represent the shunt capacitance for the qubit and the coupling capacitance between the qubit and the transmission line, respectively. Φ is the external magnetic flux threading the SQUID (Superconducting QUantum Interference Device) loop and JJ denotes the Josephson junctions. b Comparison of a π-pulse with and without the cancellation when the qubit is tuned away. The input pulse is suppressed by −33.5 dB with a cancellation pulse with 5.12 × 105 averages. c Comparison between the canceled π-pulse from b and the photon emission by the qubit (red line) after a π/2-pulse with the pulse cancellation on. The red line is a fit to an exponential decay to extract Γ2/(2π) = 193 ± 4 kHz.
