In this paper we study the generation of photon pairs through the process of spontaneous four wave mixing (SFWM) in a χ (3) cavity. Our key interest is the generation of photon pairs in a guided-wave configuration—fiber or waveguide—where at least one of the photons in a given pair is matched in frequency and bandwidth to a particular atomic transition, as required for the implementation of photon–atom interfaces. We present expressions, along with plots, for the two-photon joint intensity both in the spectral and temporal domains. We also present expressions for the absolute brightness, along with numerical simulations, and show that the presence of the cavity can result in a flux enhancement relative to an equivalent source without a cavity.
In this paper we study the generation of photon pairs through the process of spontaneous four wave mixing (SFWM) in a χ (3) cavity. Our key interest is the generation of photon pairs in a guided-wave configuration—fiber or waveguide—where at least one of the photons in a given pair is matched in frequency and bandwidth to a particular atomic transition, as required for the implementation of photon–atom interfaces. We present expressions, along with plots, for the two-photon joint intensity both in the spectral and temporal domains. We also present expressions for the absolute brightness, along with numerical simulations, and show that the presence of the cavity can result in a flux enhancement relative to an equivalent source without a cavity.
We introduce a new kind of spontaneous four wave mixing process for the generation of photon pairs, in which the four waves involved counter-propagate in a guided-wave medium; we refer to this process as counter-propagating spontaneous four wave mixing (CP-SFWM). We show that for the simplest CP-SFWM source, in which all waves propagate in the same polarization and transverse mode and in which self- and cross-phase modulation effects are negligible, phasematching is attained automatically regardless of dispersion in the fiber or waveguide. Furthermore, we show that in two distinct versions of this source (both pumps pulsed, or one pump pulsed and the remaining one monochromatic), the two-photon state is automatically factorable provided that the length of the nonlinear medium exceeds a certain threshold, easily achievable in practice since this threshold length tends to be in the range of mm to cm. We also show that if one of the pumps approaches the monochromatic limit, and for a sufficient nonlinear medium length, the bandwidth of one of the two photons in a given pair may be reduced to the level of MHz, compatible with electronic transitions for the implementation of atom–photon interfaces, without the use of optical cavities.
We study the processes of spontaneous four wave mixing and of third-order spontaneous parametric downconversion in optical fibers, as the basis for the implementation of photon-pair and photon-triplet sources. We present a comparative analysis of the two processes including expressions for the respective quantum states and plots of the joint spectral intensity, a discussion of phasematching characteristics, and expressions for the conversion efficiency. We have also included a comparative study based on numerical results for the conversion efficiency for the two sources, as a function of several key experimental parameters.
Quantum entanglement has been an extremely active field of research, both theoretically and experimentally. Studies on entanglement are fundamental to improving our basic understanding of quantum mechanics. As our understanding of the phenomenon grows, so does interest in using it to advance various technological fields: communications, computing, and sensing, to name just a few. It is now known that entangled photon pairs can be generated through a process known as Spontaneous Four-Wave Mixing (SFWM). In this paper, we report the generation of entangled photon pairs in time intervals by spontaneous four-wave mixing in a nonlinear fiber optic ring resonator. The requirements for efficient SFWM are quite similar to those for classical FWM, but they require even greater precision, especially for quantum applications. To achieve a measurable pair generation rate, a high-intensity pump laser is essential. The nonlinear medium must have high nonlinearity and confinement. This technique is compatible with contemporary fiber, enabling compact, low-cost, and scalable implementations such as quantum memories.
We present a theoretical and experimental study of the generation of photon pairs through the process of spontaneous four-wave mixing (SFWM) in a few-mode, birefringent fiber. Under these conditions, multiple SFWM processes are in fact possible, each associated with a different combination of transverse modes for the four waves involved. We show that in the weakly guiding regime, for which the propagation modes may be well approximated by linearly polarized modes, the departure from circular symmetry due to the fiber birefringence translates into conservation rules, which retain elements from azimuthal and rectangular symmetries: both OAM and parity must be conserved for a process to be viable. We have implemented a SFWM source based on a bowtie birefringent fiber, and have measured for a collection of pump wavelengths the SFWM spectra of each of the signal and idler photons in coincidence with its partner photon. We have used this information, together with knowledge of the transverse modes into which the signal and idler photons are emitted, as input for a genetic algorithm, which accomplishes two tasks: (i) the identification of the particular SFWM processes that are present in the source, and (ii) the characterization of the fiber used.
A single atom undergoing spontaneous four-wave mixing near a chiral waveguide can efficiently channel an emitted Stokes-anti-Stokes photon pair into two tightly confined waveguide modes, yielding thus enhanced biphoton generation without requiring loss suppression or stringent phase matching. We develop a perturbative treatment, valid for a four-level atomic system under experimentally realistic conditions, to explain physical origins and clarify relevant constraints of such an enhancement determined by the interplay of atomic decay rates toward guided and unguided modes. Besides achieving optimal generation rates equivalent to a cold atomic ensemble hundreds of micrometers long in free space, our biphoton source naturally fulfills key requirements for next-generation on-chip quantum light sources, namely low-loss operation, robustness, compactness, and scalability.
We study both experimentally and theoretically the generation of photon pairs by spontaneous four-wave mixing (SFWM) in standard birefringent optical fibers. The ability to produce a range of two-photon spectral states, from highly correlated (entangled) to completely factorable, by means of cross-polarized birefringent phase matching, is explored. A simple model is developed to predict the spectral state of the photon pair which shows how this can be adjusted by choosing the appropriate pump bandwidth, fiber length and birefringence. Spontaneous Raman scattering is modeled to determine the tradeoff between SFWM and background Raman noise, and the predicted results are shown to agree with experimental data.