We report an interference experiment of spontaneous emission of light from two distant solid-state ensembles of atoms that are coherently excited by a short laser pulse. The ensembles are Erbium ions doped into two LiNbO3 crystals with channel waveguides, which are placed in the two arms of a Mach-Zehnder interferometer. The light that is spontaneously emitted after the excitation pulse shows first-order interference. By a strong collective enhancement of the emission, the atoms behave as ideal two-level quantum systems and no which-path information is left in the atomic ensembles after emission of a photon. This results in a high fringe visibility of 95%, which implies that the observed spontaneous emission is highly coherent.
We theoretically discuss one-photon and two-photon double-slit interferences for spontaneous and stimulated parametric down-conversions. We show that the two-photon sub-wavelength interference can exist in a general spontaneous parametric down-conversion (SPDC) for both type I and type II crystals. We propose an alternative way to observe sub-wavelength interference by a joint-intensity measurement which occurs for only type I crystal in a higher gain of SPDC. When a signal beam injects into the crystal, it may create two interference patterns by two stimulated down-converted beams, showing no…
Recent work using spontaneous parametric down-conversion (SPDC) has made possible investigations of the Einstein-Podolsky-Rosen paradox in its original (position-momentum) form. We propose an experiment that uses SPDC photon pairs to measure through which slit a photon passes while simultaneously observing double-slit interference.
We implement experimentally a method to generate photon-number$-$path and polarization entangled photon pairs using ``beamlike'' type-II spontaneous parametric down-conversion (SPDC), in which the signal-idler photon pairs are emitted as two separate circular beams with small emission angles rather than as two diverging cones.
We study first-order interference in spontaneous parametric down-conversion generated by two pump pulses that do not overlap in time. The observed modulation in the angular distribution of the signal detector counting rate can only be explained in terms of a quantum mechanical description based on biphoton states. The condition for observing interference in the signal channel is shown to depend on the parameters of the idler radiation.
We discuss an experimental setup where two laser-driven atoms spontaneously emit photons and every photon causes a ``click'' at a point on a screen. By deriving the probability density for an emission into a certain direction from basic quantum mechanical principles we predict a spatial interference pattern. Similarities and differences with the classical double-slit experiment are discussed.
We demonstrate one- and two-photon diffraction and interference experiments utilizing parametric down-converted photon pairs (biphotons) and a transmission grating. With two-photon detection, the biphoton exhibits a diffraction-interference pattern equivalent to that of an effective single particle that is associated with half the wavelength of the constituent photons. With one-photon detection, however no diffraction-interference pattern is observed. We show that these phenomena originate from the spatial quantum correlation between the down-converted photons.
We study the resonance fluorescence from a coherently driven four-level atom in the Y-type configuration. The effects of quantum interference induced by spontaneous emission on the fluorescence properties of the atom are investigated. It is found that the quantum interference resulting from cascade emission decays of the atom leads to a splitting of resonances in the excited level populations calculated as a function of light detuning. For some parameters, interference assisted enhancement of inner sidebands and narrowing of central peaks may also occur in the fluorescence spectrum. We present…
We study the effect of quantum interference on the structure and properties of spontaneous and stimulated transitions in a degenerate V-type three-level atom with an arbitrary total momentum of each state. Explicit expressions for the factors in the terms of the relaxation operator and stimulated transition operator with account of quantum interference effects are obtained. It has been demonstrated that the condition for the dipole transition moments to be parallel is insufficient and for conventional atoms the interference cross terms are zeros for both operators. The conditions when quantum …
We study spontaneous emission from an atom under the action of laser fields. We consider two different energy level diagrams. The first one consists of two levels resonantly driven by laser radiation where either of levels may decay to a separate level. For such a system we show that the presence of the second decay channel may deteriorate the destructive interference occurring in case of one decay channel because of Autler-Townes effect. The second diagram represents two two-level resonantly driven systems with the upper levels decaying to a common level. For this diagram we show that there i…
We show that the quantum interference between downconverted photon pairs and photons from coherent laser light can produce a maximally path entangled N-photon output component with a fidelity greater than 90% for arbitrarily high photon numbers. A simple beam splitter operation can thus transform the 2-photon coherence of down-converted light into an almost optimal N-photon coherence.
Studying the spontaneous emission of a V-type three-level atom embedded in a photonic crystal (PC) by fractional calculus, we found that the atomic excited states in the anisotropic PC can be expressed as a superposition of four dressed states analytically. Through detuning two allowed atomic transition energies with respect to the photonic band edge, the coupling between these two transitions leads to three dynamic regimes, namely non-Markovian decay, damped quantum interference and quantum interference, classified by the numbers of contributed bounded dressed states. From the degree of quant…
The spontaneous emission is investigated for an effective atomic two-level system in an intense coherent field with frequency lower than the vacuum-induced decay width. As this additional low-frequency field is assumed to be intense, multiphoton processes may be induced, which can be seen as alternative transition pathways in addition to the simple spontaneous decay. The interplay of the various interfering transition pathways influences the decay dynamics of the two-level system and may be used to slow down the spontaneous decay considerably. We derive from first principles an expression for …
We theoretically investigate nonresonant spontaneous bremsstrahlung in the scattering of an electron by a nucleus in the field of two linearly polarized light waves propagating in the same direction in the general relativistic case. It is demonstrated that there are two substantially different kinematic ranges: the noninterference range, where the Bunkin-Fedorov quantum parameters serve as multiphoton parameters,and the interference range, where interference effects become significant, and quantum interference parameters play the role of multiphoton parameters. We determine the cross sections …
Resonant spontaneous bremsstrahlung of an electron scattered by a nucleus in the field of two moderately strong pulsed laser waves is studied theoretically. The process is studied in detail within the interference kinematic region. This region is determined by scattering of particles in the same plane at predetermined angles, at that stimulated absorption and emission of photons of external pulsed waves by an electron occurs in correlated manner. The correspondence between the emission angle and the final-electron energy is established in the kinematic region where the resonant parametric inte…
High-visibility interference of photon echoes generated in spatially separated solid-state atomic ensembles is demonstrated. The solid state ensembles were LiNbO$_3$ waveguides doped with Erbium ions absorbing at 1.53 $μ$m. Bright coherent states of light in several temporal modes (up to 3) are stored and retrieved from the optical memories using two-pulse photon echoes. The stored and retrieved optical pulses, when combined at a beam splitter, show almost perfect interference, which demonstrates both phase preserving storage and indistinguishability of photon echoes from separate optical memo…
As a fundamental postulate of quantum mechanics, Born's rule assigns probabilities to the measurement outcomes of quantum systems and excludes multi-order quantum interference. Here we report an experiment on a single spin in diamond to test Born's rule by inspecting the third-order quantum interference. The ratio of the third-order quantum interference to the second-order in our experiment is ceiled at the scale of $10^{-3}$, which provides a stringent constraint on the potential breakdown of Born's rule.
We discuss the spontaneous emission from a coherently prepared and microwave driven doublet of potentially closely spaced excited states to a common ground level. Multiple interference mechanisms are identified which may lead to fluorescence inhibition in well-separated regions of the spectrum or act jointly in cancelling the spontaneous emission. In addition to phase independent quantum interferences due to combined absorptions and emissions of driving field photons, we distinguish two competing phase dependent interference mechanisms as means of controlling the fluorescence. The indistinguis…
In this work, the effects of quantum interference and spontaneously generated coherence (SGC) are theoretically analyzed in a four level system of a $^{87}\mathrm{Rb}$ atom. For the effects of SGC, we find that a new kind of EIT channel can be induced due to destructive interference, and the nonlinear Kerr absorption can be coherently narrowed or eliminated under different strengths of the coupling and switching fields.
The ability to entangle distant quantum nodes is essential for the construction of quantum networks and for quantum information processing. For solid-state quantum emitters used as qubits, it can be achieved by photon interference. When the emitter is subject to spectral diffusion, this process can become highly inefficient, impeding the achievement of scalable quantum technologies. We study two-photon interference in the context of a Hong-Ou-Mandel (HOM)-type experiment for two separate quantum emitters, with different detunings with respect to a specific target frequency. We evaluate the sec…
Quantum nonlinear interferometers (QNIs) can measure the infrared physical quantities of a sample by detecting visible photons. A QNI with Michelson geometry based on the spontaneous parametric down-conversion in a second-order nonlinear crystal is studied systematically. A simplified theoretical model of the QNI is presented. The interference visibility, coherence length, equal-inclination interference, and equal-thickness interference for the QNI are demonstrated theoretically and experimentally. As an application example of the QNI, the refractive index and the angle between two surfaces of…
We consider regimes of Spontaneous Parametric Down-Conversion both noncollinear and nondegenerate in frequencies. Parameters characterizing degrees of noncollinearity and of nondgeneracy are defined, and they are shown to be not independent of each other. At a given degree of nondegeneracy the emitted photons are shown to propagate along two different cones opening angles of which are determined by the degree of nondegeneracy. Based on this, the degree of nondegeneracy can be controlled by means of the angular selection of photons, e.g., with the help of appropriately installed slits. For such…
We investigate theoretically the non-Markovian dynamics of a degenerate V-type quantum emitter in the vicinity of a metallic nanosphere, a system that exhibits quantum interference in spontaneous emission due to the anisotropic Purcell effect. We calculate numerically the electromagnetic Green's tensor and employ the effective modes differential equation method for calculating the quantum dynamics of the emitter population, with respect to the resonance frequency and the initial state of the emitter, as well as its distance from the nanosphere. We find that the emitter population evolution var…
We investigate the dynamical behavior of the atom-photon entanglement in a V-type three-level quantum system using the atomic reduced entropy. It is shown that an atom and photons are entangled at the steady-state; however disentanglement can also be achieved in an especial condition. It is demonstrated that in the presence of quantum interference induced by spontaneous emission, the reduced entropy and the atom-photon entanglement are phase-dependent. Non-stationary solution is also obtained when the quantum interference due to the spontaneous emission is completely included.
Implementations of solid state quantum optics provide us with devices where qubits are placed at fixed positions in photonic or plasmonic one dimensional waveguides. We show that solely by controlling the position of the qubits and with the help of a coherent driving, collective spontaneous decay may be engineered to yield an entangled mesoscopic steady-state. Our scheme relies on the realization of pure superradiant Dicke models by a destructive interference that cancels dipole-dipole interactions in one-dimension.
As one of the central topics in quantum optics, collective spontaneous emission such as superradiance has been realized in a variety of systems. This work proposes an innovative scheme to coherently control collective emission rates via a self-interference mechanism in a nonlinear waveguide setting. The self-interference is made possible by photon backward scattering incurred by quantum scatterers in a waveguide working as quantum switches. Whether the interference is constructive or destructive is found to depend strongly on the distance between the scatterers and the emitters. The interferen…
Quantum memories for light, which allow the reversible transfer of quantum states between light and matter, are central to the development of quantum repeaters, quantum networks, and linear optics quantum computing. Significant progress has been reported in recent years, including the faithful transfer of quantum information from photons in pure and entangled qubit states. However, none of these demonstrations confirm that photons stored in and recalled from quantum memories remain suitable for two-photon interference measurements, such as C-NOT gates and Bell-state measurements, which constit…
The spontaneous decay of a V-type three-level atom placed in a negative-refractive-index waveguide is analyzed. We find that in thin waveguides, highly efficient surface guided modes are supported, which do not occur in positive index waveguides. In addition, at low absorption, the mode density and thus spontaneous emission into particular regular guided modes is enhanced by several orders of magnitude as compared to regular dielectric waveguides. The asymmetries between emission into the different modes and the enhancement of particular guided modes allow to induce strong spontaneous-emission…
It is a long standing question whether or not one can change the nature of spontaneous emission by a free electron through shaping the electron wavefunction. On one hand, shaping the electron wavefunction changes the respective charge and current densities of the electron. On the other hand, spontaneous emission of an electron is an incoherent process and can often be insensitive to the shape of the electron wavefunction. In this work, we arrive at an affirmative answer examining Bremsstrahlung radiation by free electron superposition states. We find that the radiation can be markedly differen…
We investigate the generation and the evolution of two-mode continuous-variable (CV) entanglement from system of a microwave-driven V-type atom in a quantum beat laser. By taking into account the effects of spontaneously generated quantum interference between two atomic decay channels, we show that the CV entanglement with large mean number of photons can be generated in our scheme, and the property of the filed entanglement can be adjusted by properly modulating the frequency detuning of the fields. More interesting, it is found that the entanglement can be significantly enhanced by the spont…
We consider a quantum mechanical model for the high-order harmonic generation in bulk solids. The bandgap is assumed to be considerably larger than the exciting photon energy. Using dipole approximation, the dynamical equations for different initial Bloch states are decoupled in the velocity gauge. Although there is no quantum mechanical interference between the time evolution of different initial states, the complete harmonic radiation results from the interference of fields emitted by all the initial (valence band) states. In particular, this interference is shown to be responsible for the s…
We discuss the connection between quantum interference effects in optical beams and radiation fields emitted from atomic systems. We illustrate this connection by a study of the first- and second-order correlation functions of optical fields and atomic dipole moments. We explore the role of correlations between the emitting systems and present examples of practical methods to implement two systems with non-orthogonal dipole moments. We also derive general conditions for quantum interference in a two-atom system and for a control of spontaneous emission. The relation between population trapping…
We investigate the question whether Michelson type interferometry is possible if the role of the beam splitter is played by a spontaneous process. This question arises from an inspection of trajectories of atoms bouncing inelastically from an evanescent-wave (EW) mirror. Each final velocity can be reached via two possible paths, with a {\it spontaneous} Raman transition occurring either during the ingoing or the outgoing part of the trajectory. At first sight, one might expect that the spontaneous character of the Raman transfer would destroy the coherence and thus the interference. We investi…
Enhanced Emission and Two-Photon Interference of Lead-Vacancy Centers in Diamond Solid Immersion Lenses
Institute of Science Tokyo（东京科学大学）；National Institute of Advanced Industrial Science and Technology（产业技术综合研究所）；National Institute for Materials Science（国立材料研究所）；National Institutes for Quantum Science and Technology（量子科学技术研究开发机构）
We consider a pair of three-level atoms interacting with the vacuum. The process of disentanglement due to spontaneous emission and the role of quantum interference between principal transitions in this process, are analysed. We show that the presence of interference can slow down disentanglement. In the limit of maximal interference, some part of initial entanglement can survive.
With quantum interference of two-path spontaneous emissions, we propose a novel scheme to coherently control the atom--photon momentum entanglement through atomic internal coherence. A novel phenomenon called ``momentum phase entanglement'' is reported, and we found, under certain conditions, that more controllable entangled state can be produced with super--high degree of entanglement.
In a previous paper [B. Deb and G. S. Agarwal, Phys. Rev. A 90, 063417 (2014)], it was theoretically shown that, magneto-optical manipulation of low energy scattering resonances and atom-molecule transitions could lead to the formation of a bound state in continuum (BIC), provided there is no spontaneous emission. We find that even an exceedingly small spontaneous decay from exited molecular states can spoil the BIC. In this paper, we show how to circumvent the detrimental effect of spontaneous emission by making use of vacuum-induced coherence (VIC) which results in the cancellation or suppre…
In the present work, we derive a formalism that can be used to predict and interpret the time structure and achievable visibilities for two-photon interference (TPI) experiments using photons from two separate sources. The treatment particularly addresses photons stemming from solid state quantum emitters, which are often subject to pure dephasing (PD) and spectral diffusion (SD). Therefore, it includes the impact of phase- and emission frequency-jitter besides the influence of differing radiative lifetimes and a relative spectral detuning. While the treatment is mainly aimed at interference e…
Here we demonstrate generating and storing entanglement in a solid state spin-wave quantum memory with on-demand read out using the process of rephased amplified spontaneous emission (RASE). Amplified spontaneous emission (ASE), resulting from an inverted ensemble of Pr$^{3+}$ ions doped into a Y$_2$SiO$_5$ crystal, generates entanglement between collective states of the praseodymium ensemble and the output light. The ensemble is then rephased using a four-level photon echo technique. Entanglement between the ASE and its echo is confirmed and the inseparability violation preserved when the RAS…
Stimulated emission of two photons is observed experimentally in the parametric amplification process and is compared to a three-photon interference scheme. We find that the underlying physics of stimulated emission is simply the constructive interference due to photon indistinguishability. So the observed signal enhancement upon the input of photons is a result of multi-photon interference of the input photons and the otherwise spontaneously emitted photon from the amplifier.
In spontaneous parametric down conversion (SPDC) based quantum information processing (QIP) experiments, there is a tradeoff between the coincide count rates (i.e. the pumping power of the SPDC), which limits the rate of the protocol, and the visibility of the quantum interference, which limits the quality of the protocol. This tradeoff is mainly caused by the multi-photon pair emissions from the SPDCs. In theory, the problem is how to model the experiments without truncating these multi-photon emissions while including practical imperfections. In this paper, we establish a method to theoretic…
The fluorescence light emitted by a 4-level system in $J=1/2$ to $J=1/2$ configuration driven by a monochromatic laser field and in an external magnetic field is studied. We show that the spectrum of resonance fluorescence emitted on the $π$ transitions shows a signature of spontaneously generated interference effects. The degree of interference in the fluorescence spectrum can be controlled by means of the external magnetic field, provided that the Landé g-factors of the excited and the ground state doublet are different. For a suitably chosen magnetic field strength, the relative weight of t…
We find an interference effect for electron-phonon interactions in coupled semiconductor quantum dots that can dominate the nonlinear transport properties even for temperatures close to zero. The intradot electron tunnel process leads to a `shake up' of the phonon system and is dominated by a double-slit-like interference effect of spontaneously emitted phonons. The effect is closely related to subradiance of photons (Dicke effect) in a laser-trapped two-ion system and explains the oscillations in the nonlinear current-voltage characteristics of coupled dots observed recently.
We study the spectral properties of Spontaneous Parametric Down Conversion in a periodically poled waveguided structure of KTP crystal pumped by ultra-short pulses. Our theoretical analysis reveals a strongly multimode and asymmetric structure of the two-photon spectral amplitude for type-II SPDC. Experimental evidence, based on Hong-Ou-Mandel polarization interference with narrowband filtering, confirms this result.
Spontaneous Raman emission in atomic gases provides an attractive source of photon pairs with a controllable delay. We show how this technique can be implemented in solid state systems by appropriately shaping the inhomogeneous broadening. Our proposal is eminently feasible with current technology and provides a realistic solution to entangle remote rare-earth doped solids in a heralded way.
We report generation of a new quantum interference effect in spontaneous emission from a resonantly driven system of two identical two-level atoms due to the spatial variation of the laser phase at the positions of the atoms. This interference affects significantly the spectral features of the emitted radiation and the quantum entanglement in the system. The interference leads to dynamic coupling of the populations and coherences in a basis, determined by the laser phase and represents a kind of vacuum mediated super-exchange between the symmetric and antisymmetric states.
Amplified spontaneous emission is a common noise source in active optical systems, it is generally seen as being an incoherent process. Here we excite an ensemble of rare earth ion dopants in a solid with a π-pulse, resulting in amplified spontaneous emission. The application of a second π-pulse leads to a coherent echo of the amplified spontaneous emission that is correlated in both amplitude and phase. For small optical thicknesses, we see evidence that the amplified spontaneous emission and its echo are entangled.
For the solid state double-dot interferometer, the phase shifted interference pattern induced by the interplay of inter-dot Coulomb correlation and multiple reflections is analyzed by harmonic decomposition. Unexpected result is uncovered, and is discussed in connection with the which-path detection and electron loss.
A universal and fault tolerant scheme for quantum computation is proposed which utilizes a class of error correcting codes that is based on the detection of spontaneous emission (of, e.g., photons, phonons, and ripplons). The scheme is compatible with a number of promising solid-state and quantum-optical proposals for quantum computer implementations, such as quantum dots in cavities, electrons on helium, and trapped ions.
We consider multimode two-photon interference at a beam splitter by photons created by spontaneous parametric down-conversion. The resulting interference pattern is shown to depend upon the transverse spatial symmetry of the pump beam. In an experiment, we employ the first-order Hermite-Gaussian modes in order to show that, by manipulating the pump beam, one can control the resulting two-photon interference behavior. We expect these results to play an important role in the engineering of quantum states of light for use in quantum information processing and quantum imaging.
Quantum networks require interfacing stationary and flying qubits. These flying qubits are usually nonclassical states of light. Here we consider two of the leading source technologies for nonclassical light, spontaneous parametric down-conversion and single semiconductor quantum dots. Down-conversion delivers high-grade entangled photon pairs, whereas quantum dots excel at producing single photons. We report on an experiment that joins these two technologies and investigates the conditions under which optimal interference between these dissimilar light sources may be achieved.
The visibilities of second-order (single-photon) and fourth-order (two-photon) interference have been observed in a Young's double-slit experiment using light generated by spontaneous parametric down-conversion and a photon-counting intensified CCD camera. Coherence and entanglement underlie one-and two-photon interference, respectively. As the effective source size is increased, coherence is diminished while entanglement is enhanced, so that the visibility of single-photon interference decreases while that of two-photon interference increases. This is the first experimental demonstration of t…
We report on an experimental observation of a two-photon ghost interference experiment. A distinguishing feature of our experiment is that the photons are generated via a non-degenerated spontaneous four-wave mixing process in a hot atomic ensemble; therefore the photon has narrow bandwidth. Besides, there is a large difference in frequency between two photons in a pair. Our works may be important to achieve more secure, large transmission capacity long-distance quantum communication.
In the quest to realize a scalable quantum network, semiconductor quantum dots (QDs) offer distinct advantages including high single-photon efficiency and indistinguishability, high repetition rate (tens of GHz with Purcell enhancement), interconnectivity with spin qubits, and a scalable on-chip platform. However, in the past two decades, the visibility of quantum interference between independent QDs rarely went beyond the classical limit of 50$\%$ and the distances were limited from a few meters to kilometers. Here, we report quantum interference between two single photons from independent QD…
Using spontaneous parametric down conversion and a 50:50 beam splitter, we generate coaxial polarization-entangled photon pairs, of which the two photons are far separated from each other. The photons are then sent one by one through one port of a modified Mach-Zehnder interferometer. We observe interference fringes with a periodicity half of the single-photon wavelength, independent of the distance between the photons. This feature can find applications in quantum-enhanced measurement.
We propose a scheme to create distant entangled atomic states. It is based on driving two (or more) atoms with a weak laser pulse, so that the probability that two atoms are excited is negligible. If the subsequent spontaneous emission is detected, the entangled state is created. We have developed a model to analyze the fidelity of the resulting state as a function of the dimensions and location of the detector, and the motional properties of the atoms.
We investigate the spontaneous emission from an inverted Y-type atomic system coupled by three coherent fields. We use the Schrödinger equation to calculate the probability amplitudes of the wave function of the system and derive an analytical expression of the spontaneous emission spectrum to trace the origin of the spectral features. Quantum interference effects, such as the spectral line narrowing, spectrum splitting and dark resonance are observed. The number of spectral components, the spectral linewidth, and relative heights can be very different depending on the physical parameters. A v…
