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arXiv:2502.18670 · Physical Review A

Programmable interferometer: An application in quantum channels

J. S. Araújo, K. Khan, A. S. Coelho

Published Jun 30, 2025• 0 citations
arXivHTMLPDF

Abstract

Quantum optics plays a crucial role in developing quantum computers on different platforms. In photonics, precise control over light's degrees of freedom, including discrete variables (polarization, photon number, orbital angular momentum) and continuous variables (phase, amplitude quadratures, frequency), is fundamental. Our model manipulates photonic systems to encode and process quantum information via the photon's spatial degree of freedom, employing polarization as an auxiliary qubit. We propose a programmable photonic circuit that simulates quantum channels, including phase-damping, amplitude-damping, and bit-flip channels, through adjustable interferometric parameters. Furthermore, the interferometer extends to complex channels, such as the squeezed generalized amplitude damping. This work contributes to advancing quantum simulation techniques and serves as a foundation for exploring quantum computing applications, while highlighting pathways for their practical implementation.

DOI
10.1103/x2px-wvcr

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Quantum optics plays a crucial role in developing quantum computers on different platforms. In photonics, precise control over light's degrees of freedom, including discrete variables (polarization, photon number, orbital angular momentum) and continuous variables (phase, amplitude quadratures, frequency), is fundamental. Our model manipulates photonic systems to encode and process quantum information via the photon's spatial degree of freedom, employing polarization as an auxiliary qubit. We propose a programmable photonic circuit that simulates quantum channels, including phase-damping, amplitude-damping, and bit-flip channels, through adjustable interferometric parameters. Furthermore, the interferometer extends to complex channels, such as the squeezed generalized amplitude damping. This work contributes to advancing quantum simulation techniques and serves as a foundation for exploring quantum computing applications, while highlighting pathways for their practical implementation.
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Quantum technologies are rapidly emerging as a foundation for next-generation information processing, communication, and sensing. In particular, optical platforms stand out as a promising avenue for scalable and efficient architectures. Here, information can be encoded either in discrete variables (DV)—such as polarization, path, frequency, or angular momentum—or in continuous variables (CV) of the optical field, such as quadratures. We develope a new formalism for the joint description of multiphoton and multimode light undergoing Gaussian transformations, and we use it to explore two DV-CV hybrid protocols. The first unifies and extends distinct forms of boson sampling, merging DV scattershot boson sampling with CV Gaussian boson sampling, thereby enabling quantum advantage demonstrations with squeezed photons. The second protocol deals with the Bell state measurement (BSM) for qudits, which are a higher-dimensional generalization of the qubit. Bell measurements play a key role in fusion-based quantum computation entanglement distribution and secret key sharing. We therefore introduce high-dimensional BSMs through linear interferometry combined with multiple single-mode squeezers, outperforming state-of-the-art theoretical methods in linear optics without using auxiliary states. This result shows how bridging the DV and CV paradigms provides a framework in which their combined strengths can outperform their standalone applications and overcome their individual limitations.
Programmable photonics can find applications in myriad areas including the quantum information field, which encompasses communications, computing, sensing and tomography. Large-scale bulk optics setups previously prevented the development of more complex and scalable quantum optics configurations. Linear optic systems with the required fidelity require a strict control of interference through demanding phase stability mechanisms. Integrating a considerable number of photonic elements on a chip in order to implement multi-port interferometers has become the only viable technological path towards quantum information systems. This chapter introduces the applications of programmable photonics to quantum information systems. After introducing the general framework of a programmable quantum photonic system integrated on a chip and briefly describing the role of more external components such as sources and detectors, it covers the relationship between reconfigurable integrated optic circuits and linear optical quantum gates, quantum transport simulation, boson sampling and complex Hadamard and quantum Fourier transforms.
Spatial light modulators are versatile devices employed in a vast range of applications to modify the transverse phase or amplitude profile of an incident light beam. Most experiments are designed to use a specific polarization which renders optimal sensitivity for phase or amplitude modulation. Here we take a different approach and apply the formalism of quantum information to characterize how a phase modulator affects a general polarization state. In this context, the spatial modulators can be exploited as a resource to couple the polarization and the transverse spatial degrees of freedom. Using a quasimonochromatic single-photon beam obtained from a pair of twin photons generated by spontaneous parametric down conversion, we performed quantum process tomography in order to obtain a general analytic model for a quantum channel that describes the action of the device on the polarization qubits. We illustrate the application of these concepts by demonstrating the implementation of a controllable phase flip channel. This scheme can be applied in a straightforward manner to characterize the resulting polarization states of different types of phase or amplitude modulators and motivates the combined use of polarization and spatial degrees of freedom in innovative applications.
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