We report the first experimental observations of two-photon emission from semiconductors, to the best of our knowledge, and develop a corresponding theory for the room-temperature process. Spontaneous two-photon emission is demonstrated in optically-pumped bulk GaAs and in electrically-driven GaInP/AlGaInP quantum wells. Singly-stimulated two-photon emission measurements demonstrate the theoretically predicted two-photon optical gain in semiconductors - a necessary ingredient for any realizations of future two-photon semiconductor lasers. Photon-coincidence experiment validates the simultaneity of the electrically-driven GaInP/AlGaInP two-photon emission, limited only by detector's temporal resolution.
When basic tools of quantum information are applied to the quantum tomography data presented in Nature 439, 179 (2006), none of their devices appears to be a source of entangled photons.
We propose a compact high-intensity room-temperature source of entangled photons based on the efficient second-order process of two-photon spontaneous emission from electrically-pumped semiconductor quantum wells in a photonic microcavity. Two-photon emission rate in room-temperature semiconductor devices is determined solely by the carrier density, regardless of the residual one-photon emission. The microcavity selects two-photon emission for a specific signal and idler wavelengths and at a preferred direction without modifying the overall rate. Pair-generation rate in GaAs/AlGaAs quantum wel…
We demonstrate quantum interference between photons generated by the radiative decay processes of excitons that are bound to isolated fluorine donor impurities in ZnSe/ZnMgSe quantum-well nanostructures. The ability to generate single photons from these devices is confirmed by auto-correlation experiments, and indistinguishability of single photons from two independent devices is confirmed via a Hong-Ou-Mandel dip. These results indicate that donor impurities in appropriately engineered semiconductor structures can portray atom-like homogeneity and coherence properties, potentially enabling sc…
It is shown that spectrally resolved photon-statistics measurements of the resonance fluorescence from realistic semiconductor quantum-dot systems allow for high contrast identification of the two-photon strong-coupling states. Using a microscopic theory, the second-rung resonance is analyzed and optimum excitation conditions are determined. The computed photon-statistics spectrum displays gigantic, experimentally robust resonances at the energetic positions of the second-rung emission.
In this chapter we review the use of semiconductor quantum dots as sources of quantum light. Principally, we focus on resonant two-photon excitation, which is a method that allows for on-demand generation of photon pairs. We explore the advantages of resonant excitation and present a number of measurements that were made in this excitation regime. In particular, we cover the following topics: photon statistics, coherent manipulation of the ground-excited state superposition, and generation of time-bin entangled photon pairs.
We experimentally demonstrate an integrated semiconductor ridge microcavity source of counterpropagating twin photons at room temperature in the telecom range. Based on parametric down conversion with a counterpropagating phase-matching, pump photons generate photon pairs with an efficiency of about 10^(-11) and a spectral linewidth of 0.3 nm for a 1mm long sample. The indistiguishability of the photons of the pair are measured via a two-photon interference experiment showing a visibility of 85%. This work opens a route towards new guided-wave semiconductor quantum devices.
In this paper we analyze the security of the so-called quantum tomographic cryptography with the source producing entangled photons via an experimental scheme proposed in Phys. Rev. Lett. 92, 37903 (2004). We determine the range of the experimental parameters for which the protocol is secure against the most general incoherent attacks.
Lasers and LEDs display a statistical distribution in the number of photons emitted in a given time interval. New applications exploiting the quantum properties of light require sources for which either individual photons, or pairs, are generated in a regulated stream. Here we review recent research on single-photon sources based on the emission of a single semiconductor quantum dot. In just a few years remarkable progress has been made in generating indistinguishable single-photons and entangled photon pairs using such structures. It suggests it may be possible to realise compact, robust, LED…
We propose an on-demand single photon source for quantum cryptography using a metal-insulator-semiconductor quantum dot capacitor structure. The main component in the semiconductor is a p-doped quantum well, and the cylindrical gate under consideration is only nanometers in diameter. As in conventional metal-insulator-semiconductor capacitors, our system can also be biased into the inversion regime. However, due to the small gate area, at the onset of inversion there are only a few electrons residing in a quantum dot. In addition, because of the strong size quantization and large Coulomb energ…
We report upon a novel principle for realization of a fast nondeterministic random number generator whose randomness relies on intrinsic randomness of the quantum physical processes of photonic emission in semiconductors and subsequent detection by the photoelectric effect. Timing information of detected photons is used to generate binary random digits-bits. The bit extraction method based on restartable clock theoretically eliminates both bias and autocorrelation while reaching efficiency of almost 0.5 bits per random event. A prototype has been built and statistically tested.
We discuss the observability of strong coupling between single photons in semiconductor microcavities coupled by a chi(2) nonlinearity. We present two schemes and analyze the feasibility of their practical implementation in three systems: photonic crystal defects, micropillars and microdisks, fabricated out of GaAs. We show that if a weak coherent state is used to enhance the chi(2) interaction, the strong coupling regime between two modes at different frequencies occupied by a single photon is within reach of current technology. The unstimulated strong coupling of a single photon and a photon…
Generating entangled photons from a monolithic chip is a major milestone towards real-life applications of optical quantum information processing including quantum key distribution and quantum computing. Ultrabroadband entangled photons are of particular interest to various applications such as quantum metrology and multi-party entanglement distribution. In this work, we demonstrate the direct generation of broadband wavelength multiplexed polarization entangled photons from a semiconductor chip for the first time. Without the use of any on-chip compensation, interferometry, entangled photons …
The realisation of a triggered entangled photon source will be of great importance in quantum information, including for quantum key distribution and quantum computation. We show here that: 1) the source reported in ``A semiconductor source of triggered entangled photon pairs''[1. Stevenson et al., Nature 439, 179 (2006)]} is not entangled; 2) the entanglement indicators used in Ref. 1 are inappropriate, relying on assumptions invalidated by their own data; and 3) even after simulating subtraction of the significant quantity of background noise, their source has insignificant entanglement.
We report the generation of polarization-entangled photons, using a quantum dot single photon source, linear optics and photodetectors. Two photons created independently are observed to violate Bell's inequality. The density matrix describing the polarization state of the postselected photon pairs is also reconstructed, and agrees well with a simple model predicting the quality of entanglement from the known parameters of the single photon source. Our scheme provides a method to generate no more than one entangled photon pair per cycle, a feature useful to enhance quantum cryptography protocol…
We demonstrate and characterize interference between discrete photons emitted by two separate semiconductor quantum dot states in different samples excited by a pulsed laser. Their energies are tuned into resonance using strain. The photons have a total coalescence probability of 18.1% and the coincidence rate is below the classical limit. Post-selection of coincidences within a narrow time window increases the coalescence probability to 47%. The probabilities are reduced from unity because of dephasing and the postselection value is also reduced by the detector time response.
Single photons from solid-state quantum emitters are playing a crucial role in the development of photonic quantum technologies. Higher order states, such as N-photon Fock-states allow for applications e.g. in quantum-enhanced sensing. In this study, we utilize the dispersion of a hot cesium vapor at the D1 lines to realize a temporal delay for one and two-photon Fock-states as a result of the slow-light effect. Single photons are generated on-demand from an InGaAs quantum dot, while their quantum interference at a beam splitter is used to generate a two-photon Fockstate. We verify the success…
We report on a fast, bandwidth-tunable single-photon source based on an epitaxial GaAs quantum dot. Exploiting spontaneous spin-flip Raman transitions, single photons at $780\,$nm are generated on-demand with tailored temporal profiles of durations exceeding the intrinsic quantum dot lifetime by up to three orders of magnitude. Second-order correlation measurements show a low multi-photon emission probability ($g^{2}(0)\sim\,0.10-0.15$) at a generation rate up to $10\,$MHz. We observe Raman photons with linewidths as low as $200\,$MHz, narrow compared to the $1.1\,$GHz linewidth measured in re…
We present a semiconductor master equation technique to study the input/output characteristics of coherent photon transport in a semiconductor waveguide-cavity system containing a single quantum dot. We use this approach to investigate the effects of photon propagation and anharmonic cavity-QED for various dot-cavity interaction strengths, including weakly-coupled, intermediately-coupled, and strongly-coupled regimes. We demonstrate that for mean photon numbers much less than 0.1, the commonly adopted weak excitation (single quantum) approximation breaks down, even in the weak coupling regime.…
Sources of non-classical light are of paramount importance for future applications in quantum science and technology such as quantum communication, quantum computation and simulation, quantum sensing and quantum metrology. In this review we discuss the fundamentals and recent progress in the generation of single photons, entangled photon pairs and photonic cluster states using semiconductor quantum dots. Specific fundamentals which are discussed are a detailed quantum description of light, properties of semiconductor quantum dots and light-matter interactions. This includes a framework for the…
The semiconductor diode, which acts as an electrical rectifier and allows unidirectional electronic transports, is the key to information processing in integrated circuits. Analogously, an optical rectifier (or diode) working at specific target wavelengths has recently becomes a dreaming device in optical communication and signal processing. In this paper, we propose a scheme to realize an optical diode for photonic transport at the level of few photons. The system consists of two spatially overlapping single-mode semiconductor microcavities coupled via ${χ^{(2)}}$ nonlinearities. The photon b…
From the microscopic quantum Langevin equations (QLEs) we derive the effective semiconductor QLEs and the associated noise correlations which are valid at a low-injection level and in real devices. Applying the semiconductor QLEs to semiconductor light-emitting devices (LEDs), we obtain a new formula for the Fano factor of photons which gives the photon-number statistics as a function of the pump statistics and several parameters of LEDs. Key ingredients are non-radiative processes, carrier-number dependence of the radiative and non-radiative lifetimes, and multimodeness of LEDs. The formula i…
Parametric downconversion (PDC) in semiconductor Bragg-reflection waveguides (BRW) is routinely exploited for photon-pair generation in the telecommunication range. Contrary to many conventional PDC sources, BRWs offer possibilities to create spectrally broadband but nevertheless indistinguishable photon pairs in orthogonal polarizations that simultaneously incorporate high frequency entanglement. We explore the characteristics of co-propagating twin beams created in a type-II ridge BRW. Our PDC source is bright and efficient, which serves as a benchmark of its performance and justifies its ex…
General expressions are obtained for the coefficient of light absorption by free carriers as well as the intensity of the spontaneous light emission by hot electrons in multivalley semiconductors. These expressions depend on the electron concentration and electron temperature in the individual valleys. An anisotropy of the dispersion law and electron scattering mechanisms is taken into account. Impurity-related and acoustic scattering mechanisms are analyzed. Polarization dependence of the spontaneous emission by hot electrons is found out. At unidirectional pressure applied or high irradiatio…
For the visualization of quantum states, the approach based on Wigner functions can be very effective. Homodyne detection has been extensively used to obtain the density matrix, Wigner functions and tomographic reconstructions of optical fields for many thermal, coherent or squeezed states. Here, we use time-domain optical homodyne tomography for the quantum state recognition and reconstruction of the femtosecond optical field from a nonequilibrium superradiant coherent electron-hole state formed in a semiconductor laser structure. We observe severe deviations from the Poissonian statistics of…
We theoretically investigate polarization-entangled photon generation by using a semiconductor quantum dot embedded in a microcavity. The entangled states can be produced by the application of two cross-circularly polarized laser fields. The quantum dot nanostructure is considered as a four-level system (ground, two excitons and bi-exciton states) and the theoretical study relies on the dressed states scheme. The quantum correlations, reported in terms of the entanglement of formation, are extensively studied for several values of the important parameters of the quantum dot system as the bi-ex…
Entanglement is one of the most fascinating properties of quantum mechanical systems; when two particles are entangled the measurement of the properties of one of the two allows to instantaneously know the properties of the other, whatever the distance separating them. In parallel with fundamental research on the foundations of quantum mechanics performed on complex experimental set-ups, we assist today to a bourgeoning of quantum information technologies bound to exploit entanglement for a large variety of applications such as secure communications, metrology and computation. Among the differ…
We propose and design a high-brightness, ultra-compact electrically pumped GaSb-based laser source of entangled photons generated by mode-matched intracavity parametric down-conversion of lasing modes. To describe the nonlinear mixing in highly dispersive and dissipative waveguides, we develop a nonperturbative quantum theory of parametric down-conversion of waveguide modes which takes into account the effects of modal dispersion, group and phase mismatch, propagation, dissipation, and coupling to noisy reservoirs. We extend our theory to the regime of quantized pump fields with a new approach…
The angular dependences of the spontaneous emission by hot electrons in multivalley semiconductors are studied theoretically and experimentally using $n$-Ge as an example. We demonstrate that the change in the scattering mechanism caused by the growth of electron temperature can affect the angular scattering dependence. In the case when the heating field is applied along the symmetry axis of the crystal [for $n$-Ge it is the axis (1,0,0,)], the angular dependence of the emission was observed experimentally for the first time, and the corresponding theory is proposed. When electrons have identi…
As single-photon sources become more mature and are used more often in quantum information, communications and measurement applications, their characterization becomes more important. Single-photon-like light is often characterized by its brightness, and two quantum properties: the single-photon composition and the photon indistinguishability. While it is desirable to obtain these quantities from a single measurement, currently two or more measurements are required. Here, we simultaneously determine the brightness, the single photon purity, the indistinguishability, and the statistical distrib…
We investigate exciton emission of quantum well embedded in a semiconductor microcavity. The analytical expressions of the light intensity for the cases of excitonic number state and coherent state are presented by using secular approximation. Our results show that the effective exciton-exciton interaction leads to the appearance of collapse and revival of the light intensity. The revival time is twice compared the coherent state case with that of the number state. The dissipation of the exciton-polariton lowers the revival amplitude but does not alter the revival time. The influences of the d…
Semiconductor's energy band and its degeneracy are altered when an external magnetic field varies, analogously to the appearance of Landau levels. Such alternation leads to the variation of energy levels and thus quantum-mechanical instability. As a consequence, spontaneous photon emission and/or paramagnetically screening effect take place. By computing total energy variation, we discuss why these effects are bound to occur. In addition, we calculate the rate and spectrum of spontaneous photon emission, which can be experimentally tested.
Most optical quantum devices require deterministic single-photon emitters. Schemes so far demonstrated in the solid state imply an energy relaxation which tends to spoil the coherent nature of the time evolution, and with it the photon indistinguishability. We focus our theoretical investigation on semiconductor quantum dots embedded in microcavities. Simple and general relations are identified between the photon indistinguishability and the collection efficiency. The identification of the key parameters and of their interplay provides clear indications for the device optimization.
The dependence of the excitonic two-photon absorption on the quantum correlations (entanglement) of exciting biphotons by a semiconductor quantum well is studied. We show that entangled photon absorption can display very unusual features depending on space-time-polarization biphoton parameters and absorber density of states for both bound exciton states as well as for unbound electron-hole pairs. We report on the connection between biphoton entanglement, as quantified by the Schmidt number, and absorption by a semiconductor quantum well. Comparison between frequency-anti-correlated, unentangle…
We consider theoretically a closed (zero-dimensional) semiconductor microcavity where confined vacuum photonic mode is coupled to electrons in valence band of the semiconductor. It is shown that vacuum-induced virtual electron transitions between valence and conduction bands result in renormalization of electron energy spectrum. As a consequence, vacuum-induced band gaps appear within the valence band. Calculated values of the band gaps are of sub-meV scale, that makes this QED effect to be measurable in state-of-the-art experiments.
As a high-order quantum transition, two-photon emission has an extremely low occurrence rate compared to one-photon emission, thus having been considered a forbidden process. Here, we propose a scheme that allows ultrafast two-photon emission, leveraging highly confined surface plasmon polariton modes in a degenerately-doped, light-emitting semiconductor thin film. The surface plasmon polariton modes are tailored to have simultaneous spectral and spatial overlap with the two-photon emission in the semiconductor. Using degenerately-doped InSb as the prototype material, we show that the two-phot…
The simplest approach to deal with light excitations in direct-gap semiconductors is to model them as a two-band system: one conduction and one valence band. For such models, particularly simple analytical expressions are known to exist for the optical response such as multi-photon absorption coefficients. Here we show that generic multi-band models do not require much more complicated expressions. Our length-gauge analysis is based on the semiconductors Bloch equations in the absence of all scattering processes. In the evaluation, we focus on two-photon excitation by a pump-probe scheme with …
The implementation of a fully integrated Hadamard gate on one single chip is currently one of the major goals in the quantum computation and communication community. Prerequisites for such a chip are the integration of single-photon sources and detectors into waveguide structures such as photonic crystals or slab and ridge waveguide. Here, we present an implementation of a single-photon on-chip experiment based on a III-V semiconductor platform. Individual semiconductor quantum dots were used as pulsed single-photon sources integrated in ridge waveguides, and on-chip waveguide-beamsplitter ope…
We demonstrate on chip generation of correlated pairs of photons in the near-visible spectrum using a CMOS compatible PECVD Silicon Nitride photonic device. Photons are generated via spontaneous four wave mixing enhanced by a ring resonator with high quality Q-factor of 320,000 resulting in a generation rate of 950,000 $\frac{pairs}{mW}$. The high brightness of this source offers the opportunity to expand photonic quantum technologies over a broad wavelength range and provides a path to develop fully integrated quantum chips working at room temperature.
We study a new effect of Cooper-pair-based two-photon gain in semiconductor-superconductor structures, showing broadband enhancement of ultrafast two-photon amplification. We further show that with the superconducting enhancement, at moderately high seed intensities the two-photon gain contribution approaches that of the one-photon gain. A full quantum-optical model of singly- and fully-stimulated two-photon emission is developed. Our results provide new insights on nonlinear light-matter interaction in the superconducting state, including the possibility of coherent control in two-photon semi…
Tomographic analysis demonstrates that the polarization state of pairs of photons emitted from a biexciton decay cascade becomes entangled when spectral filtering is applied. The measured density matrix of the photon pair satisfies the Peres criterion for entanglement by more than 3 standard deviations of the experimental uncertainty and violates Bell's inequality. We show that the spectral filtering erases the ``which path'' information contained in the photons color and that the remanent information in the quantum dot degrees of freedom is negligible.
We propose a compact and highly-efficient scheme for complete Bell-state analysis using two-photon absorption in a superconducting proximity region of a semiconductor avalanche photodiode. One-photon transitions to the superconducting Cooper-pair based condensate in the conduction band are forbidden, whereas two-photon transitions are allowed and are strongly enhanced by superconductivity. This Cooper-pair based two-photon absorption results in a strong detection preference of a specified entangled state. Our analysis shows high detection purity of the desired Bell state with negligible false …
We study theoretically the photon statistics of the field emitted from two optically coupled semiconductor microcavities each containing a quantum well. The emission is determined by the interplay between exciton-photon coupling in each quantum well and internal interaction between the two optically coupled microcavities. A high degree of coherent control and tunability via the quantum well-cavity coupling strength and photon tunneling over the photon statistics of the transmitted field can be achieved. We demonstrate that the optical property of radiation emitted by one quantum well can be co…
We present quantum Maxwell-Bloch equations (QMBE) for spatially inhomogeneous optical semiconductor devices taking into account the quantum noise effects which cause spontaneous emission and amplified spontaneous emission. Analytical expressions derived from the QMBE are presented for the spontaneous emission factor beta and the far field pattern of amplified spontaneous emission in broad area quantum well lasers.
The photon statistics and bunching of a semiconductor laser with external optical feedback are investigated experimentally and theoretically. In a chaotic regime, the photon number distribution is measured and undergoes a transition from Bose-Einstein distribution to Poisson distribution with increasing the mean photon number. The second order degree of coherence decreases gradually from 2 to 1. Based on Hanbury Brown-Twiss scheme, pronounced photon bunching is observed experimentally for various injection currents and feedback strengths, which indicates the randomness of the associated emissi…
We perform extended numerical studies to maximize the overall photon coupling efficiency of fiber-coupled quantum dot single-photon sources emitting in the near-infrared and telecom regime. Using the finite element method, we optimize the photon extraction and fiber-coupling efficiency of quantum dot single-photon sources based on micromesas, microlenses, circular Bragg grating cavities and micropillars. The numerical simulations which consider the entire system consisting of the quantum dot source itself, the coupling lens, and the single-mode fiber yield overall photon coupling efficiencies …
Using a polaron master equation approach we investigate the resonance fluorescence spectra from coherently driven quantum dots (QDs) coupled to an acoustic phonon bath and a photonic crystal waveguide with a rich local density of photon states (LDOS). Resonance fluorescence spectra from QDs in semiconductor crystals are known to show strong signatures of electron-phonon interactions, but when coupled to a structured photonic reservoir, the QD emission properties are also determined by the frequency dependence of the LDOS of the photon reservoir. Here, we investigate the simultaneous role of co…
We show that superradiant emission (SR) in semiconductor laser diode structures is governed by the master equation of the form of Ginzburg-Landau equation or Gross-Pitaevskii equation for a phase transition to coherent matter state. We conjectured condensation of one-dimensional longitudinal lower polaritons with effective mass of 10$^{-11}$ the mass of free electron. Two different regimes of SR emission and polariton condensation are predicted, one of which exhibits some characteristic features of the Dicke superradiance in atomic gases. The predictions of analytic model are confirmed by the …
We demonstrate background-free quantum frequency conversion of single photons from an epitaxially-grown InAs quantum dot. Single photons at \approx 980 nm are combined with a pump laser near 1550 nm inside a periodically-poled lithium niobate (PPLN) waveguide, generating single photons at \approx 600 nm. The large red-detuning between the pump and signal wavelengths ensures nearly background-free conversion, avoiding processes such as upconversion of anti-Stokes Raman scattered pump photons in the PPLN crystal. Second-order correlation measurements on the single photon stream are performed bot…
Transferring entangled states between photon pairs is essential for quantum communication technologies. Semiconductor quantum dots are the most promising candidate for generating polarization-entangled photons deterministically. Recent improvements in photonic quality and brightness now make them suited for complex quantum optical purposes in practical devices. Here we demonstrate for the first time swapping of entangled states between two pairs of photons emitted by a single quantum dot. A joint Bell measurement heralds the successful generation of the Bell state $Ψ^+$ with a fidelity of up t…
Quantum state engineering, the cornerstone of quantum photonic technologies, mainly relies on spontaneous parametric down-conversion and four-wave mixing, where one or two pump photons decay into a photon pair. Both these nonlinear effects require momentum conservation (i.e., phase-matching) for the participating photons, which strongly limits the versatility of the resulting quantum states. Nonlinear metasurfaces, due to their subwavelength thickness, relax this constraint and extend the boundaries of quantum state engineering. Here, we generate entangled photons via spontaneous parametric do…
We investigate the photon statistics, entanglement and squeezing of a pn-junction sandwiched between two superconducting leads, and show that such an electrically-driven photon pump generates correlated and entangled pairs of photons. In particular, we demonstrate that the squeezing of the fluctuations in the quadrature amplitudes of the emitted light can be manipulated by changing the relative phase of the order parameters of the superconductors. This reveals how macroscopic coherence of the superconducting state can be used to tailor the properties of a two-photon state.
An outstanding goal in quantum optics and scalable photonic quantum technology is to develop a source that each time emits one and only one entangled photon pair with simultaneously high entanglement fidelity, extraction efficiency, and photon indistinguishability. By coherent two-photon excitation of a single InGaAs quantum dot coupled to a circular Bragg grating bullseye cavity with broadband high Purcell factor up to 11.3, we generate entangled photon pairs with a state fidelity of 0.90(1), pair generation rate of 0.59(1), pair extraction efficiency of 0.62(6), and photon indistinguishabili…
We revisit Mandel's notion that the degree of coherence equals the degree of indistinguishability by performing Hong-Ou-Mandel- (HOM-)type interferometry with single photons elastically scattered by a cw resonantly driven excitonic transition of an InAs/GaAs epitaxial quantum dot. We present a comprehensive study of the temporal profile of the photon coalescence phenomenon which shows that photon indistinguishability can be tuned by the excitation laser source, in the same way as their coherence time. A new figure of merit, the coalescence time window, is introduced to quantify the delay below…
It is shown that the interference between spontaneous emission into the non-lasing supermode and the laser field of a semiconductor laser array causes spatial holeburning which couples the dynamics of the spontaneous emission with the laser field. In particular, phase locking between the spontaneous emission and the lasing mode leads to the formation of a spectral triplet composed of in-phase relaxation oscillation sidebands and an out-of-phase line at the lasing frequency.
We evidence the influence of surface effects for InAs quantum dots embedded into GaAs photonic nanowires used as efficient single photon sources. We observe a continuous temporal drift of the emission energy that is an obstacle to resonant quantum optics experiments at the single photon level. We attribute the drift to the sticking of oxygen molecules onto the wire, which modifies the surface charge and hence the electric field seen by the quantum dot. The influence of temperature and excitation laser power on this phenomenon is studied. Most importantly, we demonstrate a proper treatment of t…
We show that quantum frequency conversion (QFC) can overcome the spectral distinguishability common to inhomogeneously broadened solid-state quantum emitters. QFC is implemented by combining single photons from an InAs quantum dot (QD) at 980 nm with a 1550 nm pump laser in a periodically-poled lithium niobate (PPLN) waveguide to generate photons at 600 nm with a signal-to-background ratio exceeding 100:1. Photon correlation and two-photon interference measurements confirm that both the single photon character and wavepacket interference of individual QD states are preserved during frequency c…
Single photon detectors are key for time-correlated photon counting applications [1] and enable a host of emerging optical quantum information technologies [2]. So far, the leading approach for continuous and efficient single-photon detection in the optical domain has been based on semiconductor photodiodes [3]. However, there is a paucity of efficient and continuous single-photon detectors in the microwave regime, because photon energies are four to five orders of magnitude lower therein and conventional photodiodes do not have that sensitivity. Here we tackle this gap and demonstrate how iti…
