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arXiv:2107.02740 · Optics Express

High-speed imaging of spatiotemporal correlations in Hong-Ou-Mandel interference

Xiaoqin Gao, Yingwen Zhang, Alessio D’Errico, Khabat Heshami, Ebrahim Karimi

Published May 2, 2022• 16 citations
arXivHTMLPDF

Abstract

The Hong-Ou-Mandel interference effect lies at the heart of many emerging quantum technologies whose performance can be significantly enhanced with increasing numbers of entangled modes one could measure and thus utilize. Photon pairs generated through the process of spontaneous parametric down conversion are known to be entangled in a vast number of modes in the various degrees of freedom (DOF) the photons possess such as time, energy, and momentum, etc. Due to limitations in detection technology and techniques, often only one such DOFs can be effectively measured at a time, resulting in much lost potential. Here, we experimentally demonstrate, with the aid of a time tagging camera, high speed measurement and characterization of two-photon interference. With a data acquisition time of only a few seconds, we observe a bi-photon interference and coalescence visibility of ∼64% with potentially up to ∼2 × 103 spatial modes. These results open up a route for practical applications of using the high dimensionality of spatiotemporal DOF in two-photon interference, and in particular, for quantum sensing and communication.

DOI
10.1364/oe.456433

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The Hong-Ou-Mandel interference effect lies at the heart of many emerging quantum technologies whose performance can be significantly enhanced with increasing numbers of entangled modes one could measure and thus utilize. Photon pairs generated through the process of spontaneous parametric down conversion are known to be entangled in a vast number of modes in the various degrees of freedom (DOF) the photons possess such as time, energy, and momentum, etc. Due to limitations in detection technology and techniques, often only one such DOFs can be effectively measured at a time, resulting in much lost potential. Here, we experimentally demonstrate, with the aid of a time tagging camera, high speed measurement and characterization of two-photon interference. With a data acquisition time of only a few seconds, we observe a bi-photon interference and coalescence visibility of ∼64% with potentially up to ∼2 × 103 spatial modes. These results open up a route for practical applications of using the high dimensionality of spatiotemporal DOF in two-photon interference, and in particular, for quantum sensing and communication.
Two-photon interference is widely used in quantum information processing, e.g., state engineering and designing quantum gates, as well as in quantum sensing and metrology. This includes the generation and characterization of N00N states, which provide a phase measurement sensitivity that is beyond the shot-noise limit. There have been numerous efforts in generating N00N states with a photon number higher than 2, since their measurement sensitivity increases with N. Both photon number state and modal (temporal, spectral, and spatial) properties of light offer advantages in sensing, where the latter is achieved through mode-multiplexed measurements. Here, we experimentally demonstrate, with the aid of a recently developed photon-detection technology, measurement and characterization of up to tera-mode spatiotemporal correlations in two-photon interference and use it to generate high-dimensional two-photon N00N-states, which can be advantageous for multiphase estimation. We observe a high bi-photon interference and coalescence visibility of ∼64%\sim64\%∼64% and ∼88%\sim88\%∼88% for a tera (101210^{12}1012) and 0.2 tera (2×10112\times 10^{11}2×1011) spatiotemporal modes, respectively. These results open up a route for practical applications of using the spatiotemporal degrees of freedom in two-photon interference, and in particular, for quantum sensing and communication.
Among the whole experiments using entangled pairs of photons, the famous experiment of two-photon interference known now as Hong-Ou-Mandel (HOM) interference, is probably one of the most fascinating. This ground-breaking experiment paved the way for a multitude of experiments showing the richness of the quantum properties of Spontaneous Parametric Down conversion (SPDC) and their applications to original communication protocols. Most of them use the coherence time property of a bi-photon state and measurement are mainly performed with bucket detectors and coincidence counters. While some studies report the spatial coherence of two-photon state, measurements are always performed in the temporal domain.
We report the first observation of Hong-Ou-Mandel (HOM) interference of highly indistinguishable photon pairs with spatial resolution. Direct imaging of two-photon coalescence with an intensified sCMOS camera system clearly reveals spatially separated photons appearing pairwise within one of the two modes. With the use of the camera system, we quantified the number of pairs and recovered the full HOM dip yielding 96.3% interference visibility, as well as counted the number of coalesced pairs. We retrieved the spatial modes of both interfering photons by performing a proof-of-principle demonstration of a new, low-noise, high-resolution coincidence imaging scheme.
Photons are among the most important carriers of quantum information owing to their rich degrees of freedom (DoFs), including various spatiotemporal structures. The ability to characterize these DoFs, as well as the hidden correlations among them, directly determines whether they can be exploited for quantum tasks. While various methods have been developed for measuring the spatiotemporal structure of classical light fields, owing to the technical challenges posed by weak photon flux, there have so far been no reports of observing such structures in their quantum counterparts, except for a few studies limited to correlations within individual DoFs. Here, we propose and experimentally demonstrate a self-referenced, high-efficiency, and all-optical method, termed 3D imaging of photonic wave packets, for comprehensive characterization of the spatiotemporal structure of a quantum light field, i.e., the biphoton spatiotemporal wave packet. Benefiting from this developed method, we successfully observe the spatial-spatial, spectral-spectral, and spatiotemporal correlations of biphotons generated via spontaneous parametric down-conversion, revealing rich local and nonlocal spatiotemporal structure in quantum light fields. This method will further advance the understanding of the dynamics in nonlinear quantum optics and expand the potential of photons for applications in quantum communication and quantum computing.
In this work we demonstrate spectral-temporal correlation measurements of the Hong-Ou-Mandel (HOM) interference effect with the use of a spectrometer based on a photon-counting camera. This setup allows us to take, within seconds, spectral temporal correlation measurements on entangled photon sources with sub-nanometer spectral resolution and nanosecond timing resolution. Through post processing, we can observe the HOM behaviour for any number of spectral filters of any shape and width at any wavelength over the observable spectral range. Our setup also offers great versatility in that it is capable of operating at a wide spectral range from the visible to the near infrared and does not require a pulsed pump laser for timing purposes. This work offers the ability to gain large amounts of spectral and temporal information from a HOM interferometer quickly and efficiently and will be a very useful tool for many quantum technology applications and fundamental quantum optics research.
Superposition and indistinguishablility between probability amplitudes have played an essential role in observing quantum interference effects of correlated photons. The Hong-Ou-Mandel interference and interferences of the path-entangled photon number state are of special interest in the field of quantum information technologies. However, a fully generalized two-photon quantum interferometric scheme accounting for the Hong-Ou-Mandel scheme and path-entangled photon number states has not yet been proposed. Here we report the experimental demonstrations of the generalized two-photon interferometry with both the interferometric properties of the Hong-Ou-Mandel effect and the fully unfolded version of the path-entangled photon number state using photon-pair sources, which are independently generated by spontaneous parametric down-conversion. Our experimental scheme explains two-photon interference fringes revealing single- and two-photon coherence properties in a single interferometer setup. Using the proposed interferometric measurement, it is possible to directly estimate the joint spectral intensity of a photon pair source.