Production and applications of non-Gaussian quantum states of light

Single-mode Quantum Non-Gaussian Light from Warm Atoms

“…However, for the majority of the prospective applications of quantum technologies, a mere nonclassicality cannot provide a boosting resource over the analogous classical approach, but the enhancement must be supplied by the sensitive quantum non-Gaussian (QNG) properties available either as QNG input states or through the controllable nonlinear QNG interactions [3]. By the definition, QNG states hallmark intrinsically nonlinear character of the source [4,5] and already serve as an indispensable resources for the nontrivial character of quantum sensing [6,7], and error correction [8][9][10][11], dominantly for motional states of trapped ions and microwave radiation in the superconducting circuits.…”

“…Such states of light can already find applica-tions in quantum communication and interfaces [27,28]. Although the provable QNG properties of single-photon states have been unambiguously demonstrated in several optical platforms with complementary features, the crucial ability to efficiently interact with matter and form together complex interfering quantum systems remains elusive [3,[29][30][31][32]. Importantly, utilization of QNG light in the interaction with matter requires a well defined degrees of freedom corresponding to ideally a single optical mode, which would enable an efficient excitation of atomic or solid-state transitions.…”

“…Intrinsically single-photon emitters, including single trapped cold atoms or ions, allow for a direct observability of genuine QNG properties due to a good isolation from an environment and are working in a provably close-to a single mode regime, however, typically provide either low photon rates [21] or low photon detection efficiencies [25]. QNG sources implemented by a heralded generation of states approaching single-photon Fock states in various optical nonlinear processes [3,14,20,23,24,[33][34][35] naturally allow for notably higher photon generation efficiencies assisted by a directionality of the underlying optical phase matching, however, they typically contribute with many spectral and temporal modes simultaneously. A multi-mode spectral nature of a free-space SPDC is typically unavoidable and, in addition, its certification by interferometric measurements is in feasible bandwidth regimes extremely challenging.…”

“…A conventional enhancement of modeness in these systems corresponds to a severe filtration resulting in a small two-photon coupling efficiencies accompanied by a high susceptibility of observability of QNG to residual noise. Despite significant advancements in demonstrations of operation of narrowband SPDC sources utilizing optical cavities have been demonstrated [36][37][38][39][40][41][42], with most recent works approaching a single-mode regime [43], a provable observation of a single-mode QNG light still remains an open challenge [3]. A rapid development in realization of spon-taneous four-wave mixing (SFWM) photon sources with warm atomic vapors over the past decade brought experimentally very feasible demonstrations of a rich variety of spectrally narrow-band and provably nonclassical light with strongly sub-Poissonian and anti-bunched statistics promising a natural applicability for interaction with target atomic ensembles and storage in quantum memories due to their spectral compatibility [44][45][46][47][48][49][50][51][52][53][54].…”

“…A rapid development in realization of spon-taneous four-wave mixing (SFWM) photon sources with warm atomic vapors over the past decade brought experimentally very feasible demonstrations of a rich variety of spectrally narrow-band and provably nonclassical light with strongly sub-Poissonian and anti-bunched statistics promising a natural applicability for interaction with target atomic ensembles and storage in quantum memories due to their spectral compatibility [44][45][46][47][48][49][50][51][52][53][54]. However, to unambiguously surpass the QNG thresholds [55], the combination of a residual two-photon noise component and a two-photon coupling efficiency, which are partially competing requirements, have to be established at an unprecedented level [3,55]. At the same time, the temporal and spectral modeness of the heralded fields from atomic ensembles with emission spectra dominated by a Doppler broadening in the heralded two-photon regime remains an open question.…”