Single Photons from Coupled Quantum Modes

Abstract

Single photon emitters often rely on a strong nonlinearity to make the behavior of a quantum mode susceptible to a change in the number of quanta between one and two. In most systems, the strength of nonlinearity is weak, such that changes at the single quantum level have little effect. Here, we consider coupled quantum modes and find that they can be strongly sensitive at the single quantum level, even if nonlinear interactions are modest. As examples, we consider solid-state implementations based on the tunneling of polaritons between quantum boxes or their parametric modes in a microcavity. We find that these systems can act as promising single photon emitters. Introduction.-The construction of single photon sources [1,2] is a current aim of quantum nonlinear optics. Aside from contributing to the security of quantum cryptography [3], single photon sources are useful elsewhere, for example, in schemes for quantum computation using only linear optics and photodetection [4]. For some applications, it is enough to reduce the intensity of a laser source to obtain single photons with a probability limited by the Poisson distribution. To do better than Poisson statistics, one requires some form of nonlinearity. However, when one works in the single photon regime, a strong nonlinearity is not so easy to find.In semiconductor microcavities, light is strongly coupled to quantum well excitons resulting in new quasiparticles known as polaritons. Taking the best from both parents, polaritons have attracted particular attention for over a decade due to their strong nonlinearity (inherited from excitons) as well as their fast dynamics, long coherence, and ability to couple to external light (features of photons). Polariton-polariton interactions have resulted in micron-sized optical parametric oscillators [5][6][7], optical gates [8], spontaneous coherence [9-11], low threshold lasing at room temperature [12][13][14], and superfluidity [15]. While these effects involve many polaritons at once, we wish to focus on the single quantum regime. In planar cavities, quantum effects such as squeezing have been reported and several studies on quantum correlations undertaken [16][17][18][19]. More pronounced effects at the single polariton level are expected in quantum boxes [20][21][22], where polaritons are fully confined in three dimensions and forced to interact even more strongly. Available recently, such confinement has encouraging prospects for single photon sources.It has been predicted that for a very strong nonlinearity, the presence of a single polariton can block the resonant injection of another [23], analogous to the photon blockade [24] of nonlinear cavities. However, to obtain a strong enough nonlinearity for a single photon source, an ex-

Unconventional photon blockade in doubly resonant microcavities with second-order nonlinearity

“…Finally, for optimal antibunching, the required normal mode splitting in the photonic molecule is 2J 0.4 meV with these parameters, but it could be further reduced for larger g nl /κ. As the time interval over which antibunching occurs in UPB is limited by π/J [15,17], this value implies a time resolution of roughly 10 ps for experimentally showing UPB with single-photon correlation measurements [37].…”

“…On the other hand, given the small values of typical nonlinear coefficients of most semiconducting and insulating materials [14], an unconventional photon blockade (UPB) process could facilitate achieving antibunched light emission from suitably engineered coupled modes [15]. Such mechanism is based on destructive quantum interference between distinct driven-dissipative pathways [16,17], and requires a significantly smaller optical nonlinearity than its conventional counterpart.…”

Cavity quantum electrodynamics with a single quantum dot coupled to a photonic molecule

“…Most of these proposals, for example observing the quantum phase transition of light, require a nonlinearity in each cavity, which is a formidable task with current technology. However, several proposals involving a single QD coupled to multiple cavities predict novel quantum phenomena, for example, generation of bound photon-atom states [13], or sub-Poissonian light generation in a pair of coupled cavities or in a photonic molecule containing a single QD [14,15]. This photonic molecule, coupled to a single QD, forms the first step towards building an integrated cavity network with coupled QDs.…”

Macroscopic quantum self-trapping and Josephson oscillations of exciton polaritons

“…This result opens the way to highly nonlinear photonic phenomena such as polarization chaos 13 , or spontaneous symmetry breaking and pitchfork bifurcations 17,28,29 , expected to give rise to highly squeezed macroscopic states 14 . By reducing the size of the system, the many-particle interactions evidenced here could be taken into the regime of single-photon nonlinearities 30,31 . Furthermore, the pair of coupled cavities we have used could be extended to arrays with minimal frequency dispersion, where photon fermionization 32,33 and the emergence of Bose-Hubbard physics [34][35][36][37] have been predicted.…”