Coherence-domain imaging systems can be operated in a single-photon counting mode, offering low detector noise; this in turn leads to increased sensitivity for weak light sources and weakly reflecting samples. We have demonstrated that excellent axial resolution can be obtained in a photon-counting coherence domain imaging (CDI) system that uses light generated via spontaneous parametric down-conversion (SPDC) in a chirped periodically poled stoichiometric lithium tantalate (chirped-PPSLT) structure, in conjunction with a niobium nitride superconducting single-photon detector (SSPD). The bandwidth of the light generated via SPDC, as well as the bandwidth over which the SSPD is sensitive, can extend over a wavelength region that stretches from 700 to 1500 nm. This ultra-broad wavelength band offers a near-ideal combination of deep penetration and ultra-high axial resolution for the imaging of biological tissue. The generation of SPDC light of adjustable bandwidth in the vicinity of 1064 nm, via the use of chirped-PPSLT structures, had not been previously achieved. To demonstrate the usefulness of this technique, we have constructed images for a hierarchy of samples of increasing complexity: a mirror, a nitrocellulose membrane, and a biological sample comprising onion-skin cells.
We report spontaneous parametric downconversion having an unusually wide spectral bandwidth. A collinear type-1 phase-matching configuration is employed with degeneracy near the zero group velocity dispersion frequency. With a spectral width of 1080 nm and degenerate wavelength 1885 nm, the source also emits a high flux of photon pairs constrained to a cone of only 2 degree half-angle. A rigorous theoretical approach is developed that confirms the experimental observations. The source properties are consistent with an ultra-short photon-pair correlation time and, for a narrowband pump, extreme…
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…
We study the properties of bi-squeezed tripartite Gaussian states created by two spontaneous parametric down-conversion processes that share a common idler. We give a complete description of the quantum correlations across of all partitions, as well as of the genuine multipartite entanglement, obtaining analytical expressions for most of the quantities of interest. We find that the state contains genuine tripartite entanglement, in addition to the bipartite entanglement among the modes that are directly squeezed. We also investigate the effect of homodyne detection of the photons in the common…
We introduce a theoretical framework based on Fano's theory of discrete-continuum interactions to analyze the quantum dynamics of broadband parametric downconversion (PDC) in the few-pump-photon regime of nonlinear quantum nanophotonics. Applying this unified analytic approach to 1D $χ^{(2)}$-nonlinear waveguides, we find a host of remarkable dynamical features due to the coupling of a discrete pump state to the signal continuum, from unit-efficiency (i.e., complete) downconversion when the coupling is dissipative, to Rabi-like oscillations with sub-exponential decay when it is dispersive. The…
We report on the generation of an indistinguishable heralded single-photon state, using highly nondegenerate spontaneous parametric downconversion (SPDC). Spectrally factorable photon pairs can be generated by incorporating a broadband pump pulse and a group-velocity matching (GVM) condition in a periodically-poled potassium titanyl phosphate (PPKTP) crystal. The heralding photon is in the near IR, close to the peak detection efficiency of off-the-shelf Si single-photon detectors; meanwhile, the heralded photon is in the telecom L-band where fiber losses are at a minimum. We observe spectral f…
We experimentally investigate the properties of light generated by the sequential processes of spontaneous parametric downconversion followed by upconversion. By interfering the upconverted photons with the original pump light, we show that the processes preserve the coherence of the light. Moreover, we observe interferences with doubled phase sensitivity when changing the phase of the downconverted entangled light, although its coherence length is several orders of magnitude shorter than the one of the pump light. Finally the statistics of the upconverted light is expected to be super-poisson…
We experimentally demonstrate a source of polarization entangled photon-pairs based on a single periodically-poled potassium titanyl phosphate (PPKTP) crystal pumped with a broadband, free running laser diode.The crystal is placed within a linear beam-displacement interferometer, and emits photon-pairs based ontype-0 spontaneous parametric downconversion (SPDC). We observe pair rates of 0.56 Mpairs/s/mW in a single spatial mode with a polarization visibility of 97.7% over a spectral range of 100 nm. This experiment demonstrates a pathway towards observing Gigacount rates of polarization entang…
We demonstrate sub-shot-noise photon-number correlations in a (temporal) multimode mesoscopic ($\sim 10^3$ detected photons) twin-beam produced by ps-pulsed spontaneous non-degenerate parametric downconversion. We have separately detected the signal and idler distributions of photons collected in twin coherence areas and found that the variance of the photon-count difference goes below the shot-noise limit by 3.25 dB. The number of temporal modes contained in the twin-beam, as well as the size of the twin coherence areas, depends on the pump intensity. Our scheme is based on spontaneous downco…
It is well known that the reduced state of a two-mode squeezed vacuum state is a thermal state---i.e. a state whose photon-number statistics obey a geometric distribution. More exotic \emph{broadband} states can be realized as the reduced state of two spectrally-entangled beams generated using nonlinear optics. We show that these broadband "pseudothermal" states are tensor products of states in spectral Schmidt modes, whose photon-number statistics obey a geometric distribution. We study the spectral and temporal coherence properties of these states and show that their spectral coherence can b…
High-throughput bidirectional electro-optic transduction assessed with a practical quantum capacity
JILA, National Institute of Standards and Technology and the University of Colorado（JILA，美国国家标准与技术研究院和科罗拉多大学）；Department of Physics, University of Colorado, Boulder（科罗拉多大学博尔德分校物理系）
We experimentally demonstrate a simple method to measure the biphoton joint spectrum by mapping the spectral information onto the temporal domain using a dispersive medium. Various top-hat spectral filters are used to limit the spectral (and hence, temporal) extent of the broadband downconversion photons measured. The sharp edges of the spectral filters are utilized as spectral markers for dispersion characterization of the dispersive medium. This method allows dispersion characterization and joint spectral measurement to be completed simultaneously. The joint spectrum (which extends beyond 10…
We report the results of two experiments performed with two-photon light, produced via collinear degenerate optical spontaneous parametric downconversion (SPDC), in which both second-order (one-photon) and fourth-order (two-photon) interferograms are recorded in a Mach-Zehnder interferometer (MZI). In the first experiment, high-visibility fringes are obtained for both the second- and fourth-order interferograms. In the second experiment, the MZI is modified by the removal of a mirror from one of its arms; this leaves the fourth-order interferogram unchanged, but extinguishes the second-order i…
Many applications of magnetic resonance are limited by rapid loss of spin coherence caused by large transverse relaxation rates. In nuclear magnetic resonance (NMR) of large proteins, increased relaxation losses lead to poor sensitivity of experiments and increased measurement time. In this paper we develop broadband relaxation optimized pulse sequences (BB-CROP) which approach fundamental limits of coherence transfer efficiency in the presence of very general relaxation mechanisms that include cross-correlated relaxation. These broadband transfer schemes use new techniques of chemical shift r…
The coherence properties of broadband down converted light are investigated theoretically and experimentally in both the classical and quantum mechanical frameworks. Although broadband down converted light is one-photon incoherent noise, it possesses unique two-photon coherence. Thus, for performing two-photon processes, down-converted light is equivalent to coherent ultrashort pulses in some aspects and to coherent CW laser radiation in others. This equivalence is theoretically established and experimentally demonstrated in the classical, high-power regime. Two applications that take advantag…
A thulium-doped crystal is experimentally shown to be an excellent candidate for broadband quantum storage in a solid-state medium. For the first time, nuclear spin coherence is optically excited, detected and characterized in such a crystal. The lifetime of the spin coherence -- the potential storage entity -- is measured by means of Raman echo to be about 300 $μ$s over a wide range of ground state splittings. This flexibility, attractive for broadband operation, and well fitted to existing quantum sources, results from the simple hyperfine structure, contrasting with Pr- and Eu- doped crysta…
The existence of vacuum fluctuations is one of the most important predictions of modern quantum field theory. In the vacuum state, fluctuations occurring at different frequencies are uncorrelated. However, if a parameter in the Lagrangian of the field is modulated by an external pump, vacuum fluctuations stimulate spontaneous downconversion processes, creating squeezing between modes symmetric with respect to half of the frequency of the pump. Here we show that by double parametric pumping of a superconducting microwave cavity, it is possible to generate another fundamental type of correlation…
We generate spatially multimode twin beams using 4-wave mixing in a hot atomic vapor in a phase-insensitive traveling-wave amplifier configuration. The far-field coherence area measured at 3.5 MHz is shown to be much smaller than the angular bandwidth of the process and bright twin images with independently quantum-correlated sub-areas can be generated with little distortion. The available transverse degrees of freedom form a high-dimensional Hilbert space which we use to produce quantum-correlated twin beams with finite orbital angular momentum.
In this paper, we study two-photon interference of broadband chaotic light in a Michelson interferometer with two-photon-absorption detector. The theoretical analysis is based on two-photon interference and Feynman path integral theory. The two-photon coherence matrix is introduced to calculate the second-order interference pattern with polarizations being taken into account. Our study shows that the polarization is another dimension, as well as time and space, to tune the interference pattern in the two-photon interference process. It can act as a switch to manipulate the interference process…
We investigate the nonlinear interaction between two photons in a single input pulse at an atomic two level nonlinearity. A one dimensional model for the propagation of light to and from the atom is used to describe the precise spatiotemporal coherence of the two photon state. It is shown that the interaction generates spatiotemporal entanglement in the output state similar to the entanglement observed in parametric downconversion. A method of generating photon pairs from coherent pump light using this quantum mechanical four wave mixing process is proposed.
Biphoton states of signal and idler fields--obtained from spontaneous parametric downconversion (SPDC) in the low-brightness, low-flux regime--have been utilized in several quantum imaging configurations to exceed the resolution performance of conventional imagers that employ coherent-state or thermal light. Recent work--using the full Gaussian-state description of SPDC--has shown that the same resolution performance seen in quantum optical coherence tomography and the same imaging characteristics found in quantum ghost imaging can be realized by classical-state imagers that make use of phase-…
Gravitational redshift of broadband relativistic quantum photons
Institute for Quantum Computing Analytics (PGI-12), Forschungszentrum Jülich（朱利希研究中心量子计算分析研究所）；Theoretical Physics, Universität des Saarlandes（萨尔兰大学理论物理系）；Scuola Superiore Meridionale（南方高等学院）；Istituto Nazionale di Fisica Nucleare, Sezione di Napoli（意大利国家核物理研究所那不勒斯分部）；Center for Quantum Computing, RIKEN（理研量子计算中心）；Division of Light-Matter-Interaction, Johannes Kepler Universität Linz（林茨约翰内斯开普勒大学光与物质相互作用学部）
Mid-infrared light scatters much less than shorter wavelengths, allowing greatly enhanced penetration depths for optical imaging techniques such as optical coherence tomography (OCT). However, both detection and broadband sources in the mid-IR are technologically challenging. Interfering entangled photons in a nonlinear interferometer enables sensing with undetected photons making mid-IR sources and detectors obsolete. Here we implement mid-infrared frequency-domain OCT based on ultra-broadband entangled photon pairs. We demonstrate 10 $μ$m axial and 20 $μ$m lateral resolution 2D and 3D imagin…
It is challenging for observing superbunching effect with true chaotic light, here we propose and demonstrate a method to achieve superbunching effect of the degree of second-order coherence is 2.42 with broadband stationary chaotic light based on a cascaded Michelson interferometer (CMI), exceeding the theoretical upper limit of 2 for the two-photon bunching effect of chaotic light. The superbunching correlation peak is measured with an ultrafast two-photon absorption detector which the full width at half maximum reaches about 95 fs. Two-photon superbunching theory in a CMI is developed to in…
With superconducting transmon qubits --- a promising platform for quantum information processing --- two-qubit gates can be performed using AC signals to modulate a tunable transmon's frequency via magnetic flux through its SQUID loop. However, frequency tunablity introduces an additional dephasing mechanism from magnetic fluctuations. In this work, we experimentally study the contribution of instrumentation noise to flux instability and the resulting error rate of parametrically activated two-qubit gates. Specifically, we measure the qubit coherence time under flux modulation while injecting …
A key question of quantum optics is how nonclassical bi-photon correlations at low power evolve into classical coherence at high-power. Direct observation of the crossover from quantum to classical behavior is desirable, but difficult due to the lack of adequate experimental techniques that cover the ultra-wide dynamic range in photon flux from the single photon regime to the classical level. We investigate bi-photon correlations within the spectrum of light generated by broadband four-wave mixing (FWM) over a \emph{large dynamic range of $\sim80dB$ in photon flux} across the classical-to-quan…
As a tutorial to the spatial aspects of Spontaneous Parametric Downconversion (SPDC), we present a detailed first-principles derivation of the transverse correlation width of photon pairs in degenerate collinear SPDC. This width defines the size of a biphoton birth zone, the region where the signal and idler photons are likely to be found when conditioning on the position of the destroyed pump photon. Along the way, we discuss the quantum-optical calculation of the amplitude for the SPDC process, as well as its simplified form for nearly collinear degenerate phase matching. Following this, we …
Superradiance, characterized by the collective, coherent emission of light from an excited ensemble of emitters, generates photonic signals on timescales faster than the natural lifetime of an individual atom. The rapid exchange of coherence between atomic emitters and photonic fields in the superradiant regime enables a fast, broadband quantum memory. We demonstrate this superradiance memory mechanism in an ensemble of cold rubidium atoms and verify that this protocol is suitable for pulses on timescales shorter than the atoms' natural lifetime. Our simulations show that the superradiance mem…
Broadband Purcell Filter for Fast Superconducting Qubit Reset and Readout
Key Laboratory of Atomic and Subatomic Structure and Quantum Control (South China Normal University), Ministry of Education, Guangdong Basic Research Center of Excellence for Structure and Fundamental Interactions of Matter, School of Physics, South China Normal University（华南师范大学物理学院）；International Quantum Academy（国际量子学院）；School of Emerging Technology, University of Science and Technology of China（中国科学技术大学前沿技术学院）；Southern University of Science and Technology（南方科技大学）；Institute of Micro and Nano Optoelectronics, Shenzhen University（深圳大学微纳光电子研究院）
Differing from the traditional method of achieving subwavelength interference, we have demonstrated the two-photon subwavelength interference effect of broadband chaotic light in a polarization-selective Michelson interferometer with an ultrafast two-photon absorption detector the first time, which is achieved by manipulating two-photon probability amplitudes involved in the interference. In theory, the two-photon polarization coherence matrix and probability amplitudes matrix are combined to develop polarized two-photon interference terms, which explains the experimental results well. In orde…
Seeded SU(1,1) interferometry for Fourier-domain optical coherence tomography
ICFO – Institut de Ciencies Fotoniques, The Barcelona Institute of Science and Technology（光子科学研究所，巴塞罗那科技研究所）；Department of Signal Theory and Communications, Universitat Politecnica de Catalunya（信号理论与通信系，加泰罗尼亚理工大学）
Recent efforts to produce single photons via heralding have relied on creating spectrally factorable two-photon states in order to achieve both high purity and high production rate. Through a careful multimode analysis, we find, however, that spectral factorability is not necessary. Utilizing single-mode detection, a similar or better performance can be achieved with non-factorable states. This conclusion rides on the fact that even when using a broadband filter, a single-mode measurement can still be realized, as long as the coherence time of the triggering photons exceeds the measurement win…
To implement quantum light sources based on quantum emitters in applications, it is desirable to improve the extraction efficiency of single photons. In particular controlling the directionality and solid angle of the emission are key parameters, for instance, to couple single photons into optical fibers and send the information encoded in quantum light over long distances, for quantum communication applications. In addition, fundamental studies of the radiative behavior of quantum emitters, including studies of coherence and blinking, benefit from such improved photon collection. Quantum dots…
The nature of excited states of open quantum systems produced by incoherent natural thermal light is analyzed based on a description of the generator of the dynamics. Natural thermal light is shown to generate long-lasting coherent dynamics because of (i) the super-Ohmic character of the radiation, and (ii) the absence of pure dephasing dynamics. In the presence of an environment, the long-lasting coherences induced by suddenly turned-on incoherent light dissipate and stationary coherences are established. As a particular application, dynamics in a subunit of the PC-645 light-harvesting comple…
