We provide and discuss examples of quantum circuits for simulating the behavior of optical and photonic devices, especially those present in quantum communication setups. Examples include decoherence effects in optical fibers, two-photon (Hong-Ou-Mandel) interference in a beamsplitter - including the case where multiple degrees of freedom are involved - and representation of weak coherent states. Moreover, we discuss the modelling of practical non-ideal characteristics of threshold single-photon detectors, namely, the quantum efficiency and the dark count rate.
Abstract Quantum computers can efficiently simulate quantum systems evolving according to local interactions, making them valuable for exploring quantum many-body dynamics, despite current hardware and algorithmic challenges. In this work, we address the digital quantum simulations of linear optical elements which are inherently bosonic quantum systems. We adopt an encoding scheme based on Gray code to map bosonic states to qubits, which is efficient in terms of qubits and gate counts. Using a beam splitter as a representative example, we demonstrate the construction of quantum algorithms to simulate linear optical elements in quantum computers. To validate our algorithm, we performed a digital quantum simulation of the Hong-Ou-Mandel interference, a two-photon experiment. Our simulations, conducted both in quantum simulators and IBM quantum hardwares, successfully reproduced the characteristics of Hong-Ou-Mandel interference, validating our approach.
The first section of the work investigates light modes as a means of implementing optical qubits and qudits. The modes considered are polarization mode, path mode, transverse spatial mode, frequency mode, temporal bin-mode and temporal mode. Subsequently, mathematical model of linear optical elements like beam splitters (BS) and phase shifters are deduced and their capability of representing any single qubit optical gate is exposed. Finally Knill, Laflamme and Milburn (KLM) method of using linear optical elements to promote nonlinear operations based on nonlinear (nondeterministic) sign-flip gate (NS) is explained, and designs of two qubits conditional sign flip gate (c-z1/16) and CNOT gate, both based on KLM method, are demonstrated. So, universal set of quantum gates based on linear optics is possible.
Quantum information science aims to revolutionize existing methods for manipulating data by utilizing the unique features of nonclassical physical phenomena. This control is realized over several platforms, one particular being photonics which employs state of the art fabrication techniques that achieve integrated nanocircuit components. The Hong-Ou-Mandel effect underlies the basic entangling mechanism of linear optical quantum computing, and is a critical feature in the design of nanophotonic circuits used for quantum information processing. We will present some results from an on-chip Hong-Ou-Mandel (HOM) experiment that replaces the conventional beam splitter with a more compact and highly versatile ring resonator allowing greater functionality with an expanded parameter space dubbed Hong-Ou-Mandel Manifold (HOMM). The overarching goal of this work is to demonstrate on-chip, scalable, dynamically configurable quantum-optical interconnects for integration into photonic quantum information processing devices.
We examine multiphoton interference with a symmetric
SU(N) beam splitter
SN, an extension of features of the
SU(2) 50/50 beam splitter extended Hong-Ou-Mandel (eHOM) effect, whereby one obtains a zero amplitude (probability) for the output coincidence state (defined by equal number of photons
n/N in each output port), when a total number
n of photons impinges on the
N-port device. These are transitions of the form
∣n1,n2,…,nN⟩→SN∣n/N⟩⊗N, where
n=∑i=1Nni, which generalize the Hong-Ou-Mandel (HOM) effect $|1,1\rangle \overset{S_2}{\to}|1,1\rangle $, the eHOM effect $|n_1,n_2\rangle \overset{S_2}{\to}|\tfrac{n_1+n_2}{2},\tfrac{n_1+n_2}{2}\rangle $, and the generalized HOM effect (gHOM)
∣1⟩⊗N→SN∣1⟩⊗N, which have previously been studied in the literature. The emphasis of this work is on illuminating how the overall destructive interference occurs in separate groups of destructive interferences of sub-amplitudes of the total zero amplitude. We develop symmetry properties for the generalized eHOM effect (geHOM)
∣n1,n2,…,nN⟩→SN∣n/N⟩⊗N involving a zero amplitude governed by Perm(
Λ)=0, for an appropriately constructed matrix
Λ(SN) built from the matrix elements of
SN. We develop an analytical constraint equation for Perm
(Λ) for arbitrary
N that allows us to determine when it is zero. We generalize the SU(2) beam splitter feature of central nodal line (CNL), which has a zero diagonal along the output probability distribution when one of the input states is of odd parity (containing only odd number of photons), to the general case of
N=2∗N′ where
N′∈odd.
In recent works we have explored a multi-photon extension of the celebrated two-photon Hong-Ou-Mandel (HOM) effect in which the quantum amplitudes for a two-photon input to a lossless, balanced 50:50 beamsplitter (BS) undergoes complete destructive interference. In the extended Hong-Ou-Mandel (eHOM) effect the multi-photon scattering of photons from the two input ports to the two output ports of the BS for Fock number basis input states (FS)
∣n,m⟩12 exhibit complete destructive interference pairwise within the quantum amplitudes containing many scattering components, generalizing the two-photon HOM effect. This has profound implications for arbitrary bipartite photonic input states constructed from such basis states: if the input state to one input port of the BS is of odd parity, i.e. constructed from only of odd numbers of photons, then regardless of the input state to the second 50:50 BS port, there will be a central nodal line (CNL) of zeros in the joint output probability distribution along the main diagonal for coincidence detection. The first goal of this present work is to show diagrammatically how the extended HOM effect can be seen as a succession of multi-photon HOM effects when the latter is viewed as a pairwise cancellation of mirror image scattering amplitudes. The second goal of this work is to explore considerations for the experimental realization of the extended Hong-Ou-Mandel effect. We examine the case of a single photon interfering with a coherent state (an idealized laser) on a balanced 50:50 beamsplitter and consider prospects for experimental detection of the output destructive interference by including additional effects such as imperfect detection efficiency, spatio-temporal mode functions, and time delay between the detected output photons.