Page 61 - Kaleidoscope Academic Conference Proceedings 2024

HONG-OU-MANDEL DIP MEASUREMENT OF TWO INDEPENDENT WEAK COHERENT
PULSES

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Vivek, Kumar ; Prasanta, Halder ; Arka, Mukherjee ; Luv, Goyal ; V S Vaishnavi, Adurti ; Roshan Lal, Sharma ;
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Prashant Kumar, Rathore ; Atul Kumar, Gupta ; Priya, Malpani ; Pankaj Kumar, Dalela ; Rajkumar, Upadhyay 1
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Centre for Development of Telematics
ABSTRACT probability of coming the photons from different ports is zero.
As depicted in Fig. 1, if the input (output) ports of BS are a, b
Due to the simplicity of Hong-Ou-Mandel (HOM) (c, d) then the arrival of two indistinguishable photons at the
interferometer setup, it becomes very important in various BS leads to four different possibilities such as (i) both photons
quantum-based applications, especially when the photon exit from port c (ii) both photons exit from port d (iii) one
indistinguishability is required such as measurement device (other) photon exit from port c (d) and (iv) one (other) photon
independent quantum key distribution (MDI-QKD). In the exit from port d (c). In case of indistinguishable photons, only
present work, the HOM experiment setup is designed to (i) and (ii) happens. Mathematically, it can be described as
study the quantum interference between two indistinguishable
photons (frequency, time of arrival and polarization should 1
|1, 1⟩ → √ |2, 0⟩ − |0, 2⟩ (1)
be same for both photons) coming from two independent , , ,
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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 Figure 1 – The four possible combinations when two
using single photon avalanche diode. indistinguishable photons arrive at 50:50 BS.

Keywords - Two-photon interference, indistinguishability, In 1987, HOM effect was experimentally verified by Chung
visibility, temporal overlap, polarization overlap, Ki Hong, Zhe Yu Ou and Leonard Mandel [6]. HOM effect
coincidence counts. finds applications in various domains of quantum technology
such as quantum teleportation [8], clock synchronization [9],
1. INTRODUCTION quantum state engineering, quantum key distribution (QKD),
etc. As HOM can be used for Bell state measurement
Over the last three decades, efforts are being made to (BSM), it plays a significant role in MDI QKD [10], a
understand the basic principles of quantum mechanics such quantum communication protocol which removes all detector
as superposition theoretically and experimentally, to explore side channel attacks. So, HOM plays a vital role in BSM
the possibility of the development of quantum technologies related experiments. In this work, we have performed HOM
such as quantum communication [1], quantum computing [2], experiment of weak coherent light. In our experimental setup
quantum metrology [3] and many more. Several experiments we have used photons from two independent laser sources
were performed to show the superposition principle in (attenuated) and tried to achieve their indistinguishability
quantum mechanics. The two-photon interference is basic maintaining their polarization, frequency and time of arrival
to understand the superposition [4], [5]. The two-photon at the BS identical. Photons from attenuated laser sources
interference (also known as Hong-Ou-Mandel (HOM) effect) are fed to HOM setup to achieve better visibility and
experiment [6] reveals indistinguishable photons which are a lower coincidence events. Literature enlightens that for
basic building block in various quantum-based experiments. indistinguishable weak coherent light, the HOM visibility
Also, HOM effect is not restricted to photonic systems but is 0.5 (or 50%) theoretically. In the experiment, due to
also this effect can be observed in fermionic systems, phonons imperfection of devices and other factors, it goes below 0.5
etc. As HOM effect has no classical counterpart, so it (or < 50%). The rest of the paper is organized as follows.
outperforms classical computation [7]. The HOM effect In Section 2, HOM experimental setup is explained in detail.
can be explained as, when two indistinguishable photons In Section 3, we have described our results and observations.
arrive and interfere on a 50:50 beam splitter (BS), they will Finally, we conclude in Section 4, including some future
always exit the BS together in one of the output ports. The scopes.

978-92-61-39091-4/CFP2268P @ITU 2024 – 17 – Kaleidoscope