High-quality asynchronous heralded single-photon source at telecom wavelength

Abstract

We report on the experimental realization and characterization of an asynchronous heralded single photon source based on spontaneous parametric down conversion. Photons at 1550 nm are heralded as being inside a single-mode fiber with more than 60% probability, and the multi-photon emission probability is reduced by a factor up to more than 500 compared to Poissonian light sources. These figures of merit, together with the choice of telecom wavelength for the heralded photons are compatible with practical applications needing very efficient and robust single photon sources. PACS numbers: 42.50.Ar, 42.50.Dv, 42.65.Lm, 03.67.Hk With the present development of quantum communication and computing technologies, including quantum key distribution [1] and quantum teleportation [2] the interest for true single photon sources is rising. Many different implementations have been investigated, using single molecule or atom excitation [3,4,5,6], color centers in diamonds [7,8], quantum dots [9,10,11,12,13] or pulsed parametric down conversion sources [14,15]. All theses solutions have various advantages and tradeoffs between high purity and efficient single photon production, repetition rate, wavelength of the photons, and ease of use. The aim of this paper is to show that a spontaneous parametric down conversion (SPDC) source made of a bulk non-linear cristal at room temperature and a simple basic optical setup can be used to herald single photons at telecom wavelength in a very efficient way (see figure 1). The photons are also directly available in a standard single-mode telecom optical fiber, making this source a good choice for quantum communication applications such as scalable quantum networks. In this context, the term "heralded" means that photons are not generated on demand, but instead an electric signal announces the presence of a photon in a fiber. Indeed, as photons are created in pairs, the detection of one photon can be used to announce the presence of the complementary photon [16].The source presented in this paper is an asynchronous heralded single photon source (AHSPS) because the heralding signals are not synchronized with a periodic clock, the SPDC pump being continuous. It exhibits a very good probability of producing one photon and a very low probability of producing more than one photon per heralding signal. The latter probability depends on the pump power applied to the crystal, and several measurements are presented to characterize this dependency. * Electronic address: sylvain.fasel@physics.unige.ch SPDC Source 532 nm LPF Nd:YAG KNb0 3 Asynchronous Heralded Single Photon Source TTL 810nm 1550nm Application heralded photons heralding signal DF Si APD VA DM FIG. 1: Schematic of the asynchronous heralded single photon source (DM: dichroic mirror, DF: neutral density filter for pump attenuation, LPF: low-pass pump filters, VA: variable optical fiber attenuator)Our AHSPS is made of two main parts, as depicted in figure 1. The first consists in the SPDC photon pair creation stage which consists in a typ...

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

“…There is currently pressing need for the development of integrated quantum technologies allowing for the generation and manipulation of quantum states of the electromagnetic radiation, with the ultimate goal of defining a photonic-based architecture for quantum information processing [1]. For interfacing with long distance infrastructures based on fiber-optics communication, state-of-art sources of quantum radiation have been lately developed at the typical telecommunication wavelengths, either based on heralding photons [2,3] or on artificial quantum emitters [4]. However, a source of quantum radiation that is not related to any resonant behavior of a quantum emitter, but can be engineered to operate at arbitrary wavelength and work at room temperature has not yet been realized.…”

“…It has been recently proposed that single-photon blockade could be achieved in nanostructured cavities either with second-[χ (2) ] [10] or third-order [χ (3) ] [11] nonlinear susceptibility, which can be strongly enhanced by diffraction-limited photonic confinement [12,13]. 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].…”

“…10 to obtain conventional single-photon blockade in photonic microcavities made of a high-χ (2) nonlinear material -such as, e.g., III-V semiconductors (GaAs, GaP, GaN, AlN, etc.) -and fulfilling a doubly resonant condition -i.e.…”

“…The nonlinear interaction coefficient in the second resonator can be directly determined from the material χ (2) , which makes the model suitable to describe resonators made of non-centrosymmetric materials (such as III-V semiconductors). In particular, with the simplifying assumption that fundamental and second-harmonic modes have a large spatial overlap [10], such term is approximately reduced to g nl ε 0 [ω 2 /(ε 0 ε r )] 3/2χ (2) / √ V eff , whereχ (2) gives a scalar approximation for the second-order susceptibility tensor, χ (2) ijk , coupling the relevant fundamental and second-harmonic field components, respectively [27].…”

“…In particular, with the simplifying assumption that fundamental and second-harmonic modes have a large spatial overlap [10], such term is approximately reduced to g nl ε 0 [ω 2 /(ε 0 ε r )] 3/2χ (2) / √ V eff , whereχ (2) gives a scalar approximation for the second-order susceptibility tensor, χ (2) ijk , coupling the relevant fundamental and second-harmonic field components, respectively [27]. In the latter expression, V eff is an effective volume arising from the confinement of the classical field profiles in the resonator, assumed to be described by a normalized scalar function f (r) such that |f (r)| 2 d 3 r = 1.…”