Dynamical control of quantum photon-photon interaction with phase change material

TL;DR

This work addresses how to dynamically control photon-photon interactions beyond conventional unitary optics by exploiting a phase-change material (VO$_2$) to implement tunable loss in a beam splitter. The authors experimentally realize Hong-Ou-Mandel interference with frequency-entangled photon pairs, using a VO$_2$ thin film as a beam splitter whose loss is electrically driven to switch between unitary (bosonic coalescence) and nonunitary (fermionic anti-coalescence) behavior. By tuning the phase differences between transmitted and reflected amplitudes $\phi_{rt}$ and the input entanglement phase $\phi_\omega$, they demonstrate continuous transformation between HOM dip and peak, including anomalous anti-bunching. The results show reversible, thermally driven control of photon-photon interactions, with potential applications in quantum state engineering, quantum simulation, and programmable photonic information platforms.

Abstract

Quantum interference can produce a pivotal effective photon-photon interaction, enabling the exploration of various quantum information technologies that beyond the possibilities of classical physics. While such an effective interaction is fundamentally limited to the bosonic nature of photons and the restricted phase responses from commonly used unitary optical elements, loss-induced nonunitary operation provides an alternative degree of freedom to control the quantum interference. Here, we propose and experimentally demonstrate a concise yet powerful tool to unravel fundamental features of quantum interference based on the phase change material vanadium dioxide. Since the insulator-metal transition in an elaborate vanadium dioxide thin film can create any desired particle exchange phase response, we show its tunability over the effective photon-photon interaction between paired photons that are entangled in the symmetric and anti-symmetric forms, which may introduce sophisticated nonunitary operations and functionalities into programmable optical platforms. These results provide an alternative approach to investigate the quantum light-matter interaction, and facilitate the use of quantum interference for various quantum information processing tasks such as quantum simulation and quantum computation.

Figures (5)

• Figure 1: The optical property of VO$_2$ thin film can be tuned by external thermal stimuli, where (a) most photons are transmitted and reflected, and only a small amount of photons are absorbed at low temperature, but (b) only a small amount of photons are transmitted and reflected, and more photons are absorbed at high temperature. Its critical temperature for the insulator-metal transition is near 68$^\degree$C. (b-d) The measured transmission, reflection, and absorption probabilities of the VO$_2$ thin film with a thickness of 75nm that is used in our experiment.
• Figure 2: (a,e) The input frequency entanglement is prepared in the symmetric and anti-symmetric form that can be expressed as $\lvert \Psi \rangle_{in}=(\lvert \omega_1\omega_2 \rangle\pm\lvert \omega_2\omega_1 \rangle)/\sqrt{2}$. (b-d,f-h) Schematics of the distinct HOM interference output states (as illustrated by the photons (solid blue balls) or no-photons (dotted blue circles) and associated dotted rectangles) based on insulator-metal-transition VO$_2$ thin film at zero delay when the heating temperature is 40$^\degree$C,65.5$^\degree$C, 80$^\degree$C, respectively. It corresponds to (b,f) the conventional bunching (anti-bunching) state for symmetric (anti-symmetric) and bosonic interaction, (c,g) one of the intermediate states and anyon-like interaction, and (d,h) the anomalous anti-bunching (bunching) state for symmetric (anti-symmetric) and fermion-like interaction. (i) The experimental setup of HOM interferometry. PBS, polarizing beam splitter; Quartz, compensation crystal; DM, dichromic mirror; PC, polarizing controller; DW-HWP, dual-wavelength half-wave plate; LP filter, long-pass filter; PPKTP, periodically poled potassium titanyl phosphate crystal; QWP, quarter-wave plate; TS, translation stage; BS: in-fiber beam splitter; PD, single photon detector.
• Figure 3: Experimental measurement of HOM interference patterns when heating the VO$_2$ thin films. To confirm the feasibility of controlling HOM interference by harnessing the symmetric properties of incident entanglement, symmetric entanglement with degenerate wavelengths (a-e), anti-symmetric entanglement with non-degenerate wavelengths (f-j) and symmetric entanglement with non-degenerate wavelengths (k-o) are used in our experiment. Before heating the VO$_2$ thin films, it behaves as a lossless beam splitter that works as a unitary operation, and thus the conventional HOM interference patterns corresponding to bosonic interaction are observed (a,f,k). Figures (b-d.g-i,l-n) that present the HOM interference patterns of anyon-like interaction are considered as the intermediate states. After heating the VO$_2$ thin films, it becomes a lossy beam splitter with absorption probability higher than 50% such that it works as a non-unitary operation, and thus the anomalous HOM interference patterns corresponding to fermion-like interaction are observed (e,j,o).
• Figure 4: Experimental measurement of HOM interference patterns when cooling the VO$_2$ thin film. In analogy to Fig. \ref{['figure_3']}, the VO$_2$ thin film can change from lossy beam splitter (non-unitary operation) back to lossless beam splitter (unitary operation). This confirms that this VO$_2$ phase change material can be controlled with thermal temperature in a volatile and reversible fashion.
• Figure 5: The measured $g^{(2)}(\tau=0)$ as a function of the heating temperature of VO$_2$ thin film, yielding the dynamical and reversible control of effective quantum photon-photon interaction from bosonic bunching to fermionic antibunching.