Measurement and Generation of Single Photons in a Circuit

Swarnabha Chattaraj, Anupam Madhukar

Boson sampling with array of on-demand single photons (discreet variable Fock states) as resource states provides distinct advantages in complexity scaling compared to single photon resource states mimicked by the states (continuous variable) generated in nonlinear photonics. Recent progress in realization of regular ordered array of mesa top single quantum dots (MTSQDs) enabling on-demand generation of many photon resource states with high single photon purity and indistinguishability [1,2] has opened the possibility of implementing chip-scale Boson sampling with single photons. An important question towards scale up of such circuits is how the dephasing and decay timescale of individual on-demand single photons affect the final probability distribution of the N-photon entangled state. In this work we report a framework that provides direct link between the physical sources of decoherence to the outcome of multiphoton correlation measurements. We explicitly incorporate the symmetrization of the N-photon states while accounting for the shape of the individual wave packets and dephasing. Using this framework, we show predictive estimates of the probability of generation of a 4-photon NOON state using an optical circuit initialized with 4 identical single photon wave packets, mimicking the emitted photons from MTSQD single photon sources reported in [2]. Specifically, we show how the probability of generating various 4-photon entangled states depend on the two-photon interference visibility which is determined by the pure dephasing timescale in relation to the radiative decay timescale. The results provide quantitative guidelines to measure 4 photon and higher number of entangled photon states generated in an optical circuit with on demand single photon sources and provide a link between physical processes such as temperature and the output state of the quantum optical circuits.

Per Jönsson

Andrew Houck, S. M. Girvin, Robert J. Schoelkopf

We implement a cavity quantum electrodynamics system with an electrical circuit by coupling a superconducting qubit to a transmission-line resonator. We detect the quantization of microwaves in the resonator and generate single photons on demand.

Peter Shadbolt, Maria Rodas Verde, Alberto Peruzzo +6 more

We demonstrate a reconfigurable quantum photonic circuit with eight phase shifters. We use this device to generate and characterise maximally entangled two-qubit states, violate Bell inequalities, and generate single-photon mixed states.

Andrew Houck, David Schuster, Jay Gambetta +8 more