The development of photonic-based quantum information technologies depends on the availability of devices that consistently, and with high efficiency, deterministically emit identical single photons. Furthermore, a key requirement for the implementation of fiber-based quantum secured communication protocols demands that these sources be compatible with optical fiber networks operating in the low-loss telecom C-band (λ ~ 1550 nm). Semiconductor quantum dot emitters offer on-demand operation at high rates and can be incorporated into photonic structures that allow for high efficiency collection. Through composition engineering of InAs_(x)P_(1-x) dot-in-a-rod (DROD) nanowire quantum dot structures we have previously demonstrated single photon emission from wavelengths of up to the telecom O-band. Here we show how the DROD structure can be modified to shift emission wavelength to the telecom C-band with single-photon purities of g(2)(0) = 0.062. Through further optimization of these structures, we aim to dramatically increase source brightness with the long-term goal of developing scalable and efficient C-band emitting site-selected single-photon sources.

Non-classical light emitters that can generate single photons with a negligible multiphoton probability are one of the key components for quantum information technologies. Deterministically grown III-V semiconductor nanowires containing quantum dots are gaining interest as a viable platform for quantum key distribution applications. In this talk, we will report on our recent development of the fabrication of InAsP single quantum dots embedded within InP photonic waveguide nanowires. In particular, we outline the importance of the photonic waveguide design for optimum photon generation and coupling to external optics [1]. The measured count rate dependence on normalized wire diameter, D/λ (figure 1) of the nanowire sources is consistent with calculations of the spontaneous emission rate into the fundamental HE 11 nanowire waveguide mode (Γ HE11 ). Manipulating dot growth conditions and engineering the band structure around the dot (dot-in-a-rod configuration) are applied [2] to enhance the photoluminescence emission rate at 1310 nm and 1550 nm. Single photon emission with very low multiple photon probability is demonstrated at O- and C-band [3,4]. Temperature dependent, second-order correlation measurements on the 1310 nm source show that these nanowire sources can generate single photons up to temperatures of 220 K [3]. [1] S. Haffouz, et al. , Nano Letters, 18 , 3047 (2018). [2] S. Haffouz, et al., Applied Physics Letters, 117 , 113101 (2020). [3] P. Laferriére, et al. , Nano Letters, 23, 962 (2023). [4] A.N. Wakileh, et al., arXiv:2309.13381 (2023). Figure 1

Single photons and quantum interference between indistinguishable pairs of photons are promising resources in the ongoing development of quantum information technologies. On-demand generation of such photons on a photonic integrated circuit (PIC) is desirable as it can allow for stable operation and device scalability alongside other requisite components. Solid-state two-level emitters—in particular, epitaxial semiconductor quantum dots—have demonstrated to be a good source of single photons, though efficient integration onto PICs remains a challenge. Hybrid integration of such dots into on-chip photonic circuitry can provide a basis for testing practical implementations of quantum communication devices. In this talk, I will discuss NRC's InP-based nanowire quantum dots and our work integrating these onto silicon nitride integrated photonics. The cryogenic environment poses challenges in the operation of key components such as optical phase shifters, tunable filters, and on-chip detectors. With this in mind, I will review our progress and near-term plans for realizing on-chip quantum information processing. Also examined is our recent work developing nanowire sources that emit in telecom O or C bands—a key requirement for practical long distance quantum communications—and coherent control schemes for optical pumping.

Single photon sources operating on-demand at telecom wavelengths are required in fiber-based quantum secure communication technologies. In this work, we demonstrate single photon emission from position-controlled nanowire quantum dots emitting at λ>1530 nm. Emission in the C-band is achieved by composition engineering of an InAsxP1−x dot-in-a-rod structure. Using above-band pulsed excitation, we obtain single photon purities of g(2)(0)=0.062. These results represent an important step toward the scalable manufacture of high efficiency, high rate single photon emitters in the telecom C-band.

In this paper, we present our work towards scalable quantum-tech solutions in a silicon-nitride platform. We show hybrid integration of single InAs quantum dots on a Si 3 N 4 waveguide and show that this hybridization process does not ruin the single emitter properties, and may even enhance them.

We demonstrate that, even when employing above-band excitation, photons emitted from semiconductor quantum dots can have linewidths that approach their transform-limited values. This is accomplished by using quantum dots embedded in bottom-up photonic nanowires, an approach which mitigates several potential mechanisms that can result in linewidth broadening: (i) only a single quantum dot is present in each device, (ii) dot nucleation proceeds without the formation of a wetting layer, and (iii) the sidewalls of the photonic nanowire are comprised not of etched facets, but of epitaxially grown crystal planes. Using these structures we achieve linewidths of 2x the transform limit, unprecedented for above-band excitation. We also demonstrate a highly nonlinear dependence of the linewidth on both excitation power and temperature which can be described by an independent Boson model that considers both deformation and piezoelectric exciton-phonon coupling. We find that for sufficiently low excitation powers and temperatures, the observed excess broadening is not dominated by phonon dephasing, a surprising result considering the high phonon occupation that occurs with above-band excitation.

A key resource in quantum-secured communication protocols are single photon emitters. For long-haul optical networks, it is imperative to use photons at wavelengths compatible with telecom single mode fibers. We demonstrate high purity single photon emission at 1.31 μm using deterministically positioned InP photonic waveguide nanowires containing single InAsP quantum dot-in-a-rod structures. At excitation rates that saturate the emission, we obtain a single photon collection efficiency at first lens of 27.6% and a probability of multiphoton emission of g(2)(0) = 0.021. We have also evaluated the performance of the source as a function of temperature. Multiphoton emission probability increases with temperature with values of 0.11, 0.34, and 0.57 at 77, 220 and 300 K, respectively, which is attributed to an overlap of temperature-broadened excitonic emission lines. These results are a promising step toward scalably fabricating telecom single photon emitters that operate under relaxed cooling requirements.

We demonstrate on-chip generation of indistinguishable photons based on a nanowire quantum dot. From a growth substrate containing arrays of positioned-controlled single dot nanowires, we select a single nanowire which is placed on a SiN waveguide fabricated on a Si-based chip. Coupling of the quantum dot emission to the SiN waveguide is via the evanescent mode in the tapered nanowire. Post-selected two-photon interference visibilities using continuous wave excitation above-band and into a p-shell of the dot were 100%, consistent with a single photon source having negligible multi-photon emission probability. Visibilities over the entire photon wavepacket, measured using pulsed excitation, were reduced by a factor of 5 when exciting quasi-resonantly and by a factor of 10 for above-band excitation. The role of excitation timing jitter, spectral diffusion and pure dephasing in limiting visibilities over the temporal extent of the photon is investigated using additional measurements of the coherence and linewidth of the emitted photons.

Quantum dots embedded within different photonic structures can generate single photons and entangled photon pairs efficiently and at high emission rates. We present a single photon source based on a quantum dot embedded within a nanowire waveguide fabricated using selective-area vapour-liquid-solid epitaxy. The device generates single photons at a high repetition rate limited by the quantum dot lifetime (τ ~ 1 ns) and with low multi-photon emission probability (g 2 (0) ~ 0). Furthermore, linewidths of the emitted photons approach the Fourier-transform limit when the sources are excited above-band.

We report on a platform for the production of single photon devices with a fabrication yield of 100%. The sources are based on InAsP quantum dots embedded within position-controlled bottom-up InP nanowires. Using optimized growth conditions, we produce large arrays of structures having highly uniform geometries. Collection efficiencies are as high as 83% and multiphoton emission probabilities as low as 0.6% with the distribution away from optimal values associated with the excitation of other charge complexes and re-excitation processes, respectively, inherent to the above-band excitation employed. Importantly, emission peak lines hapes have Lorentzian profiles indicating that linewidths are not limited by inhomogeneous broadening but rather pure dephasing, likely elastic carrier-phonon scattering due to a high phonon occupation. This work establishes nanowire-based devices as a viable route for the scalable fabrication of efficient single photon sources and provides a valuable resource for hybrid on-chip platforms currently being developed.

Single photons are required in many applications involving quantum information processing. Integrating such sources on chip offers enhanced stability, miniaturization, and scalability. We employ a "pick and place" technique to integrate III-V nanowire-based single-photon sources with on-chip photonic circuitry. This approach provides for efficient coupling of the quantum light generated in a photonic nanowire to a SiN-based photonic integrated circuit. We have previously demonstrated that such devices can efficiently generate single photons on chip. Here we study the potential for generating indistinguishable photons from such sources. We demonstrate post-selected two-photon interference visibilities of up to 70% between sequential photons emitted from the same quantum dot when excited above-band. These findings show that the proposed approach offers a viable route for the integration of a stable source of indistinguishable photons on chip.

We report on a platform for the production of single photon devices with a fabrication yield of 100%. The sources are based on InAsP quantum dots embedded within position-controlled bottomup InP nanowires. Using optimized growth conditions, we produce large arrays of structures having highly uniform geometries. Collection efficiencies are as high as 83% and multiphoton emission probabilities as low as 0.6% with the distribution away from optimal values associated with the excitation of other charge complexes and re-excitation processes, respectively, inherent to the aboveband excitation employed. Importantly, emission peak lineshapes have Lorentzian profiles indicating that linewidths are not limited by inhomogeneous broadening but rather pure dephasing, likely elastic carrier-phonon scattering due to a high phonon occupation. This work establishes nanowirebased devices as a viable route for the scalable fabrication of efficient single photon sources and provides a valuable resource for hybrid on-chip platforms currently being developed.

Quantum dots embedded in photonic nanowires are a promising route for generating single photons with high efficiency [1]. Integration of such sources on-chip offers enhanced stability and miniaturization, important in many applications involving the processing of quantum information. Here we demonstrate the efficient coupling of quantum light generated in a III-V photonic nanowire to a silicon-based photonic integrated circuit. The hybrid integration is based on a “pick & place” approach using a nanomanipulator in a scanning electron microscope. We demonstrate detected count rates of 1 Mcps and single photon purities >95%.

We present a compact, fibre-coupled single photon source using gradient-index (GRIN) lenses and an InAsP semiconductor quantum dot embedded within an InP photonic nanowire waveguide. A GRIN lens assembly is used to collect photons close to the tip of the nanowire, coupling the light immediately into a single mode optical fibre. The system provides a stable, high brightness source of fibre-coupled single photons. Using pulsed excitation, we demonstrate on-demand operation with a single photon purity of 98.5% when exciting at saturation in a device with a source-fibre collection efficiency of 35% and an overall single photon collection efficiency of 10%. We also demonstrate "plug and play" operation using room temperature photoluminescence from the InP nanowire for room temperature alignment.

A method to integrate nanowire-based quantum dot single photon sources on-chip using evanescent coupling is demonstrated. By deterministically placing an appropriately tapered III-V nanowire, containing a single quantum dot, on top of a silicon-based ridge waveguide, the quantum dot emission directed toward the taper can be transferred to the ridge waveguide with calculated efficiencies close to 100%. As the evanescent coupling is bidirectional, the source can be optically pumped in both free-space and through the ridge waveguide. The latter configuration paves the way toward a self-contained, all-fiber, plug-and-play solution for applications requiring a bright on-demand single photon source. Using InAsP quantum dots embedded in InP nanowire waveguides, coupling efficiencies to a SiN ridge waveguide of 74% with a single photon purity of 97% are demonstrated. The technique to demonstrate deterministic placement of single quantum emitters onto pre-fabricated waveguides is used, an important step toward the fabrication of complex quantum photonic circuits.

Through fluctuations in the local composition, InAsP quantum dots embedded within site-selected InP nanowires are observed to display biexciton binding energies spanning a range between -0.3 meV and +2.9 meV. From this range we select dots having energy-degenerate exciton and biexciton emission and observe an excitation rate-mediated transition from sub- to super-Poissonian second-order correlation statistics. Under pulsed excitation, g((2)) (tau = 0) is found to increase from 0.5 at high excitation levels, rising to 28 as the excitation is reduced by two orders of magnitude. The observed second-order correlation statistics are interpreted using both a stochastic model and a rate equation model of the competition between the various excitonic emission processes. Our results demonstrate that nanowire quantum dots represent a promising approach to the efficient generation of twin-photon states.

We report on a method for suspending two-dimensional crystal materials in an electronic circuit using an only photoresists and solvents. Graphene and NbSe${}_2$ are suspended tens of nanometers above metal electrodes with clamping diameters of several microns. The optical cavity formed from the membrane/air/metal structures enables a quick method to measure the number of layers and the gap separation using comparisons between the expected colour and optical microscope images. This characterization technique can be used with just an illuminated microscope with a digital camera which makes it adaptable to environments where other means of characterization are not possible, such as inside nitrogen glove boxes used in handling oxygen-sensitive materials.

We report on a method for fabricating electromechanical structures using two-dimensional crystal materials and an all-resist process. Graphene and NbSe${}_2$ are used as the mechanical elements in parallel plate capacitor elements with several microns of suspended diameters. The optical cavity formed from the membrane/air/metal structures enables a quick method to measure the number of layers and the gap separation using comparisons between the expected colour and optical microscope images.