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Quantum 2.0 Conference and Exhibition

Fourier state tomography of quantum light

Mohammed K. Alqedra, Pierre Brosseau, Anton N. Vetlugin, Cesare Soci, Val Zwiller

Published Jan 1, 2025• 0 citations
Publisher

Abstract

We present the first experimental demonstration of Fourier state tomography of photonic polarization states. We measure entangled pairs from a quantum dot, achieving results comparable to projective tomography with fewer components, verifying the authenticity and scalability of Fourier tomography for characterizing quantum state.
DOI
10.1364/quantum.2025.qw2b.2

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Quantum state tomography is used in quantum communication, computing, and cryptography to characterize quantum states enabling assessment and control of quantum systems. Rapidly scaling quantum technologies require fast, accurate, and simple techniques, but current tomography methods are bulky, hard to scale, and slow. To overcome these limitations, we experimentally demonstrate Fourier tomography [1], of single-photon and entangled photon pairs generated by a quantum dot. As shown in Fig. 1(a) for two-photon tomography, the setup consists of a continuously rotating quarter waveplate, a fixed linear polarizer and a single photon detector per qubit. As the waveplates rotates with different speed, we record the coincidences rate between the two detectors. This signal can be expressed as a Fourier series whose coefficients can be related to the polarization state of light. Fig. 1(b) shows the simulated coincidence rate as the waveplate rotates for input Bell states∣Φ+⟩\vert \Phi^{+}\rangle∣Φ+⟩and∣Φ−⟩\left\vert\Phi^{-}\right\rangle∣Φ−⟩. By capturing the coincidences variations as a Fourier series through a single rotating element and fixed polarizer, we simplify the tomography process, providing an accurate, and simple approach suitable for scalable quantum systems.
Traditional methods of quantum state characterization are impractical for systems of more than a few qubits due to exponentially expensive postprocessing and data storage and lack robustness against errors and noise. Here, we experimentally demonstrate self-guided quantum tomography performed on polarization photonic qubits. The quantum state is iteratively learned by optimizing a projection measurement without any data storage or postprocessing. We experimentally demonstrate robustness against statistical noise and measurement errors on single-qubit and entangled two-qubit states.
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