Climbing the Fock ladder: Advancing multiphoton state generation

Abstract

A scheme for the enhanced generation of higher photon-number states is realized, using an optical timemultiplexing setting that exploits a parametric down-conversion source for an iterative state generation. We use a quantum feedback mechanism for already generated photons to induce self-seeding of the consecutive nonlinear process, enabling us to coherently add photons to the light that propagates in the feedback loop. The addition can be carried out for any chosen number of round trips, resulting in a successive buildup of multiphoton states. Our system is only limited by loop losses. The looped design is rendered possible by a carefully engineered waveguide source that is compatible with and preserves the shape of the propagating mode. We compare the fidelities and success probabilities of our protocol with the common direct heralding of photon-number states. This comparison reveals that, for same the fidelity, our feedback-based setup significantly enhances success probabilities, being vital for an efficient utilization in quantum technologies. Moreover, quantum characteristics of the produced states are analyzed, and the flexibility of producing higher photon-number states with our setup beyond the common direct heralding is demonstrated.

Optimal transmission estimation with dark counts

“…We perform this truncation at a sufficiently large number such that we do not have to worry about edge effects where more photons arrive at the detector than can be distinguished by such; this large number is determined by the total intensity N + ν that a detector might register. Fock states up until N ≈ 4-8 have been experimentally generated [92][93][94] and dark count rates tend to be much smaller than unity, so current PNRD technologies capable of resolving 10-100 photons should all suffice to avoid edge cases. In the remaining work we truncate our sums at m = 30.…”

High-gain Spontaneous Parametric Down-conversion in Dispersive and Absorbing Nanostructured Systems

“…In the high-gain regime, the SPDC and SFWM sources can be used as sources of squeezed light, where squeezed light has wide applications in continuous variable (CV) quantum computation [10][11][12][13], quantum communication [14], as well as quantum sensing [15][16][17]. Another application of high-gain operation of such sources can be for generating multi-photon Fock states [18,19], which have applications in many branches of quantum technology as well as metrology and fundamental tests of quantum entanglement [20][21][22].…”