L. Horvath, B. C. Sanders, B. F. Wielinga
We extend the analysis of photon coincidence spectroscopy beyond bichromatic excitation and two-photon coincidence detection to include multichromatic excitation and multiphoton coincidence detection. Trichromatic excitation and three-photon coincidence spectroscopy are studied in detail, and we identify an observable signature of a triple resonance in an atom-cavity system.
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Passive optical interferometry with single photons injected into some input ports and vacuum into others is enriched by admitting polarization, thereby replacing the scalar electromagnetic description by a vector theory, with the recent triad phase being a celebrated example of this richness. On the other hand, incorporating polarization into interferometry is known to be equivalent to scalar theory if the number of channels is doubled. We show that passive multiphoton $m$ channel interferometry described by SU($m$) transformations is replaced by SU($2m$) interferometry if polarization is incl…
Photon coincidence spectroscopy relies on detecting multiphoton emissions from the combined atom-cavity system in atomic beam cavity quantum electrodynamics experiments. These multiphoton emissions from the cavity are nearly simultaneous approximately on the cavity lifetime scale. We determine the optimal time for the detection window of photon pairs in two-photon coincidence spectroscopy. If the window time is too short, some photon pairs will not be detected; if the window time is too long, too many nearly coincident independent single photons will be falsely interpreted as being a photon pa…
We show that sums of carefully chosen coincidence rates in a multiphoton interferometry experiment can be simplified by replacing the original unitary scattering matrix with a coset matrix containing $0$s. The number and placement of these $0$s reduces the complexity of each term in the sum without affecting the original sum of rates. In particular, the evaluation of sums of modulus squared of permanents is shown to turn in some cases into a sum of modulus squared of determinants. The sums of rates are shown to be equivalent to the removal of some optical elements in the interferometer.
Reconstructing the multiphoton spatial wave function with coincidence wavefront sensing
提出符合波前传感（CWS）方法重建多光子空间波函数相位，通过弱测量波前传感器进行双光子数值模拟验证，为多体量子系统表征及量子光学应用提供直接空间途径。
In this article, we introduce a quantum key distribution protocol for the line of sight channels based on coincidence measurements. We present a proof-of-concept implementation of our protocol. We show that using coincidence measurements to monitor multi-photon pulses results in a higher secure key rate over longer distances for such channels. This key rate is higher than popular implementations of quantum key distribution protocol based on BB84, for example, the GLLP analysis [Quant. Info. Comput. \textbf{4}, 325 (2004)]. In the experiment, we could generate around $74 \%$ more key bits per s…
We generate bipartite states of light which exhibit an absence of multiphoton coincidence events between two modes amid a constant background flux. These `correlated photon holes' are produced by mixing a coherent state and relatively weak spontaneous parametric down-conversion using a balanced beamsplitter. Correlated holes with arbitrarily high photon numbers may be obtained by adjusting the relative phase and amplitude of the inputs. We measure states of up to five photons and verify their nonclassicality. The scheme provides a route for observation of high-photon-number nonclassical correl…
Multiphoton Hong-Ou-Mandel Interference Enables Superresolution of Bright Thermal Sources
多光子Hong-Ou-Mandel干涉实现明亮热源的超分辨率成像，通过多光子干涉与单光子Fock态，提升成像精度并超越衍射极限。
We show that photon coincidence spectroscopy can provide an unambiguous signature of two atoms simultaneously interacting with a quantised cavity field mode. We also show that the single-atom Jaynes-Cummings model can be probed effectively via photon coincidence spectroscopy, even with deleterious contributions to the signal from two-atom events. In addition, we have explicitly solved the eigenvectors and eigenvalues of two two-level atoms coupled to a quantised cavity mode for differing coupling strengths.
Photon coincidence spectroscopy is a promising technique for probing the nonlinear regime of cavity quantum electrodynamics in the optical domain, however its accuracy is mitigated by two factors: higher-order photon correlations, which contribute to an enhanced pair count rate, and non-simultaneity of emitted photon pairs from the optical cavity. We show that the technique of photon coincidence spectroscopy is effective in the presence of these effects if the quantitative predictions are adjusted to include non-simultaneity and higher-order correlations.
Non-equilibrium photon correlations of coherently excited single quantum systems can reveal their internal quantum dynamics and provide spectroscopic access. Here we propose and discuss the fundamentals of a coherent photon coincidence spectroscopy based on the application of laser pulses with variable delay and the detection of an time-averaged two-photon coincidence rate. For demonstration, two simple but important cases, i.e., an exciton - biexciton in a quantum dot and two coupled quantum emitters, are investigated based on quantum dynamics simulations demonstrating that this nonlinear spe…
We show that shifts in locations of two-photon coincidence spectral peaks, for a bichromatically-driven two-level atom passing through a single-mode cavity, are due to competition between excitation pathways for a Jaynes-Cummings system. We also discuss an analogous shift of (single-photon) spectral peaks for a driven three-level V-system, which demonstrates that competition between excitation pathways is also important in this simple system.
We propose and demonstrate a method for measuring the joint spectrum of photon pairs via Fourier spectroscopy. The biphoton spectral intensity is computed from a two-dimensional interferogram of coincidence counts. The method has been implemented for a type-I downconversion source using a pair of common-path Mach-Zender interferometers based on Soleil compensators. The experimental results agree well with calculated frequency correlations that take into account the effects of coupling into single-mode fibers. The Fourier method is advantageous over scanning spectrometry when detectors exhibit …
Momentum-resolved photoelectron emission from xenon in colinearly polarized two-color laser fields at above-threshold ionization conditions is studied both experimentally and theoretically. We utilize phase-of-the-phase spectroscopy as recently introduced by Skruszewicz et al., Phys. Rev. Lett. 115, 043001 (2015) to analyze the dependence of the yields on the relative phase $φ$ between the fundamental and second harmonic laser fields. The resulting phase-of-phase spectra feature a characteristic checkerboard pattern, which can analytically be described within the strong-field approximation.
Experimental quantum non-Gaussian coincidences of entangled photons
研究利用单量子点产生纠缠光子对，通过CHSH-Bell因子$S=2.328\pm0.004$实验认证其量子非高斯符合特性，测得非高斯深度达$0.94\pm 0.02$ dB，并降低多光子误差，为光学传感、通信与计算提供关键资源。
We use a fiber based double slit Young interferometer for studying the far-field spatial distribution of the two-photon coincidence rate (coincidence pattern) for various quantum states with different degree of spatial entanglement. The realized experimental approach allows to characterize coincidence patterns for different states without any modifications of the setup. Measurements were carried out with path-entangled and separable states. The dependence of the coincidence pattern on the phase of the interferometer for superposition and separable states was studied. The results have implicati…
Silicon single-photon detectors (SPDs) are the key devices for detecting single photons in the visible wavelength range. Here we present high detection efficiency silicon SPDs dedicated to the generation of multiphoton entanglement based on the technique of high-frequency sine wave gating. The silicon single-photon avalanche diodes (SPADs) components are acquired by disassembling 6 commercial single-photon counting modules (SPCMs). Using the new quenching electronics, the average detection efficiency of SPDs is increased from 68.6% to 73.1% at a wavelength of 785 nm. These sine wave gating SPD…
Quantum Optical Neuron for Image Classification via Multiphoton Interference
本文提出了一种基于多光子干涉的量子光学图像分类器，通过空间可编程单光子的Hong-Ou-Mandel干涉实现无相机的图像识别，具有高精度和抗噪声能力，展示了在光限制条件下高效的信息处理方法。
Multi-photon processes are the essence of nonlinear optics. Optical harmonics generation and multi-photon absorption, ionization, polymerization or spectroscopy are widely used in practical applications. Generally, the rate of an n-photon effect scales as the n-th order autocorrelation function of the incident light, which is high for light with strong photon-number fluctuations. Therefore `noisy' light sources are much more efficient for multi-photon effects than coherent sources with the same mean power, pulse duration and repetition rate. Here we generate optical harmonics of order 2-4 from…
In quantum mechanics, photons are bosons -- there is no restriction on the number of them that occupy the same quantum state, so many of them can bunch together, and this is well known as photon bunching effect. However, photon bunching and multiphoton interference of bunched photons have never been directly observed from a broadband thermal chaotic light source. Nevertheless, it has been known that the interference intensity of a number N of bunched photons oscillates with a wavelength of N times shorter than the wavelength of the constituent single photons, which should be observable in Four…
Coherent multidimensional optical spectroscopy techniques are broadly applied across the electromagnetic spectrum ranging from NMR to the UV. These reveal properties of matter through correlation plots of signal fields generated in response to sequences of short pulses with variable delays. Here we discuss a new class of multidimensional techniques obtained by time-and-frequency resolved photon coincidence counting measurements of N photons which constitutes a 2N dimensional spectrum. A compact description of these signals is developed based on time ordered superoperators rather than the norma…
Per the fluctuation-dissipation theorem, the information obtained from spin fluctuation studies in thermal equilibrium is necessarily constrained by the system's linear response functions. However, by including weak radiofrequency magnetic fields, we demonstrate that intrinsic and random spin fluctuations even in strictly unpolarized ensembles \emph{can} reveal underlying patterns of correlation and coupling beyond linear response, and can be used to study non-equilibrium and even multiphoton coherent spin phenomena. We demonstrate this capability in a classical vapor of $^{41}$K alkali atoms,…
Single photon, emitted in a transition between two states, has a frequency distribution of intensity, which is given by Lorentzian if the transition is only naturally broadened and the period of observation $T$ is long compared to the lifetime $T_{1}$ of the excited state. However, when the observation time $T$ is short or comparable to $T_{1}$, the frequency spectrum is appreciably broadened. If only the delayed part of the emitted radiation field is detected, then the radiation spectrum does not change. However, if the radiation field is transmitted through a resonant absorber and then detec…
Entangled photon pair excitation and time-frequency-filtered multidimensional photon correlation spectroscopy as a probe for dissipative exciton kinetics
本文提出结合纠缠光子增强的窄带双激子激发与时间-频率过滤的双光子同时计数，用于研究多激子动力学，通过非经典关联制备窄带双激子分布并抑制弛豫。
Frequency-resolved N-photon correlations in the ultra-strong coupling regime
研究强耦合腔量子电动力学系统中频率分辨 N 光子相关性，揭示多光子抗聚束和聚束现象，展示对称性在光-物质相互作用中的作用。
Quantum spectroscopy was performed using the frequency-entangled broadband photon pairs generated by spontaneous parametric down-conversion. An absorptive sample was placed in front of the idler photon detector, and the frequency of signal photons was resolved by a diffraction grating. The absorption spectrum of the sample was measured by counting the coincidences, and the result is in agreement with the one measured by a conventional spectrophotometer with a classical light source.
We study spectroscopy of artificial solid-state four-level quantum system. This system is formed by two coupled superconducting flux qubits. When multiple driving frequency of the applied microwaves matches the energy difference between any two levels, the transition to the upper level is induced. We demonstrate two types of the multi-photon transitions: direct transitions between two levels and ladder-type transitions via an intermediate level. For the latter transitions, in particular, the inverse population of the excited state with respect to the ground one is realized. These processes can…
The interaction of flux qubits with a low frequency tank circuit is studied. It is shown that changes in the state of the interacting qubits influence the effective impedance of the circuit, which is the essence of the so-called impedance measurement technique. The multiphoton resonant excitations in both single flux qubits and pairs of coupled flux qubits are investigated. In particular, we compare our theoretical results with recent spectroscopy measurements, Landau-Zener interferometry, and multiphoton fringes.
Photon entanglement-enhanced multidimensional spectroscopy of exciton correlations in photosynthetic aggregates
本文提出利用纠缠光子对增强多维光谱技术，用于探测光合聚集体中激子相互作用和相关性，展示其在飞秒时间尺度上的优越性能。
We propose a novel femtosecond stimulated Raman spectroscopy (FSRS) technique that combines entangled photons with interference detection to select matter pathways and enhance the resolution. Following photo excitation by an actinic pump, the measurement uses a pair of broadband entangled photons, one (signal) interacts with the molecule together with a third narrowband pulse induces the Raman process. The other (idler) photon provides a reference for the coincidence measurement. This interferometric photon-coincidence counting detection allows to separately measure Raman gain and loss signals…
A new method for highly selective remote sensing of atmospheric trace polar molecular gases is described. Based on infrared/terahertz double resonance spectroscopic techniques, the molecule- specific coincidence between the lines of a CO2 laser and rotational-vibrational molecular absorption transitions provide two dimensions of recognition specificity: infrared coincidence frequency and the corresponding terahertz frequency whose absorption strength is modulated by the laser. Atmospheric pressure broadening expands the molecular recognition "specificity matrix" by simultaneously relaxing the …
State-Selective Ionization and Trapping of Single H$_2^+$ Ions with (2+1) Multiphoton Ionization
本文利用(2+1)共振增强多光子电离实现了单个H$_2^+$离子的振转态选择性装载，并通过量子逻辑谱验证了装载成功率和转动激发态的稳定性，为氢分子离子的高精度光谱学研究提供了高效方法。
Theory of simultaneous observation of photoelectron and emitted X-ray photon in X-ray emission spectroscopy and their entanglement
本文研究了XEPECS过程中光电子与X射线光子的纠缠特性，利用三电子sp模型和系统波函数发现光电子自旋与光子线偏振发生纠缠，并在特定角度达到最大值。
Correlated photons inspire abundance of metrology-related platforms, which benefit from quantum (anti-) correlations and outperform their classical-light counterparts. While such demonstrations mainly focus on entanglement, the role of photon exchange-phase and degree of distinguishability have not been widely utilized in quantum-enhanced applications. Using an interferometric setup we show that even at low degree entanglement, when a two-photon wave-function is coupled to matter, it is encoded with a reliable "which pathway?" information. An interferometric exchange-phase-cycling protocol is …
Development of Biphoton Entangled Light Spectroscopy (BELS) using Bell pairs
BELS通过贝尔对和双光子干涉探测材料性质，利用双光子路径和偏振关联变化建立新的纠缠增强光谱学框架，用于表征量子材料和光物质相互作用。
We study a Mach-Zehnder interferometer fed by a coherent state in one input port and vacuum in the other. We explore a Bayesian phase estimation strategy to demonstrate that it is possible to achieve the standard quantum limit independently from the true value of the phase shift and specific assumptions on the noise of the interferometer. We have been able to implement the protocol using parallel operation of two photon-number-resolving detectors and multiphoton coincidence logic electronics at the output ports of a weakly-illuminated Mach-Zehnder interferometer. This protocol is unbiased and …
Entangled photon pairs are predicted to linearize and increase the efficiency of two-photon absorption, allowing continuous wave laser diodes to drive ultrafast time-resolved spectroscopy and nonlinear processes. Despite a range of theoretical studies and experimental measurements, inconsistencies persist about the value of the entanglement enhanced interaction cross section. A spectrometer is constructed that can temporally and spectrally characterize the entangled photon state before, during, and after any potential two-photon excitation event. For the molecule Rhodamine 6G, which has a virt…
The authors demonstrate a form of two-photon-counting interferometry by measuring the coincidence counts between single-photon-counting detectors at an output port of a Mach-Zehnder Interferometer (MZI) following injection of broad-band time-frequency-entangled photon pairs (EPP) generated from collinear spontaneous parametric down conversion into a single input port. Spectroscopy and refractometry are performed on a sample inserted in one internal path of the MZI by scanning the other path in length, which acquires phase and amplitude information about the samples linear response. Phase modul…
We propose the use of heralded photons to detect Gravitational Waves (GWs). Heralded photons are those photons that, produced during a parametric downconversion process, are "labelled" by the detection and counting of coincidences of their correlated or entangled twins and therefore can be discriminated from the background noise, independently of the type of correlation/entanglement used in the setup. Without losing any generality, we illustrate our proposal with a gedankenexperiment, in which the presence of a gravitational wave causes a relative rotation of the reference frames associated to…
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