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ITU Kaleidoscope Academic Conference (ITU K)

Hong-Ou-Mandel DIP Measurement of two Independent Weak Coherent Pulses

Vivek Kumar, Prasanta Halder, Mukherjee Arka, Goyal Luv, Adurti V S Vaishnavi, Sharma Roshan Lal, Rathore Prashant Kumar, Gupta Atul Kumar, Malpani Priya, Dalela Pankaj Kumar, Upadhyay Rajkumar

Published Oct 21, 2024• 0 citations

Abstract

Due to the simplicity of Hong-Ou-Mandel (HOM) interferometer setup, it becomes very important in various quantum-based applications, especially when the photon indistinguishability is required such as measurement device independent quantum key distribution (MDI-QKD). In the present work, the HOM experiment setup is designed to study the quantum interference between two indistinguishable photons (frequency, time of arrival and polarization should be same for both photons) coming from two independent laser sources (attenuated laser). The aim is to achieve high visibility as it indicates the photon indistinguishability from two independent sources. Theoretically, the visibility is $50 \%$ for indistinguishable photons from attenuated laser sources but in the experiment, due to various devices imperfections and other factors it is less than 50%. The HOM visibility achieved from our setup is $40 \%$ tested for a distance of 20 km over standard single mode fiber (SMF). The main point to be noticed in this work is that, this experiment is performed using single photon avalanche diode.

DOI: 10.23919/ituk62727.2024.10772878

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50 \%

for indistinguishable photons from attenuated laser sources but in the experiment, due to various devices imperfections and other factors it is less than 50%. The HOM visibility achieved from our setup is

40 \%

tested for a distance of 20 km over standard single mode fiber (SMF). The main point to be noticed in this work is that, this experiment is performed using single photon avalanche diode.

Recently, the Hong–Ou–Mandel (HOM) interference between two independent weak coherent pulses (WCPs) has been paid much attention due to the measurement-device-independent (MDI) quantum key distribution (QKD). Using classical wave theory, articles reported before show that the visibility of this kind of HOM-type interference is ≤ 50%. In this work, we analyze this kind of interference using quantum optics, which reveals more details compared to the wave theory. Analyses confirm the maximum visibility of 50%. And we conclude that the maximum visibility of 50% comes from the two single-photon states in WCPs, without considering the noise. In the experiment, we successfully approach the visibility of 50% by using WCPs splitting from the single pico-second laser source and phase scanning. Since this kind of HOM interference is immune to slow phase fluctuations, both the realized and proposed experiment designs can provide stable ways of high-resolution optical distance detection.

Measurement-device-independent quantum key distribution (MDI-QKD) has garnered significant attention for enabling security-loophole-free quantum communication. Successful MDI-QKD protocols rely on performing a two-photon Bell-state measurement at an intermediate node, where achieving a high-visibility Hong-Ou-Mandel (HOM) interference pattern between two independent coherent photons is crucial. In this study, we present an approach for developing indistinguishable coherent photon sources over 50 km of optical fiber under real-world conditions. We introduce the long optical injection-locking (long-OIL) technique, which enables frequency locking between two long-distance coherent photons separated by distances exceeding the coherence length of the master laser. Utilizing the long-OIL technique, we achieved time-resolved HOM interference with a visibility of 48(2)%, which is close to the theoretical limits of 50% for two independent continuous-wave coherent photons. Our results indicate that the long-OIL platform is a promising solution for MDI-QKD with repeaterless secret-key capacity.

Hong-Ou-Mandel (HOM) interference is one of the most important experimental phenomena in quantum optics. It has drawn considerable attention with respect to quantum cryptography and quantum communication because of the advent of the measurement device independent (MDI) quantum key distribution (QKD) protocol. Here, we realize HOM interference, having a visibility of approximately 38.1%, using two independent heralded single-photon sources (HSPSs). The HOM interference between two independent HSPSs is a core technology for realizing the long-distance MDI QKD protocol, the quantum coin-tossing protocol, and other quantum cryptography protocols.

Preparation of identical independent photons is the core of many quantum applications such as entanglement swapping and entangling process. In this work, Hong-Ou-Mandel experiment was performed to evaluate the degree of indistinguishability between independent photons generated from two independent weak coherent sources working at 640 nm. The visibility was 46%, close to the theoretical limit of 50%. The implemented setup can be adopted in quantum key distribution experiments carried out with free space as the channel link, as all the devices and components used are operative in the visible range of the electromagnetic spectrum.

Hong-Ou-Mandel interferometers are valuable tools in many Quantum Information and Quantum Optics applications that require photon indistinguishability. The theoretical limit for the Hong-Ou-Mandel visibility is 0.5 for indistinguishable weak coherent photon states, but several device imperfections may hinder achieving this value experimentally. In this work, we examine the dependence of the interference visibility on various factors, including 1) detector side imperfections due to after-pulses, 2) mismatches in the intensities and states of polarization of the input signals, and 3) the overall intensity of the input signals. We model all imperfections and show that theoretical modeling is in good agreement with the experimental results.

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