Radio-Frequency Hong-Ou-Mandel Interference with Conditionally Built States

TL;DR

The paper addresses the challenge of observing quantum interference in radio frequencies by conditioning classical phase-averaged coherent states to emulate a single-photon state. It employs data-pattern tomography to represent the target state as a weighted mixture of phase-averaged coherent probes with coefficients $c_j$, including negative values realized via an ancilla. It demonstrates Hong-Ou-Mandel interference at 120 MHz, yielding dips in the normalized second-order correlation below the classical limit $0.5$, with depth tunable through the representation coefficients. The results validate conditional preparation as a scalable approach for quantum-like phenomena in spectral regions lacking practical quantum light sources and motivate future RF Bell tests and related quantum protocols.

Abstract

We report an experimental demonstration of room-temperature Hong-Ou-Mandel (HOM) interference at a radio-wave frequency of 120 MHz using conditional build-up of quantum states from classical phase-averaged coherent states. This approach enables observation of quantum effects in spectral regimes where conventional single-photon sources and detectors are unavailable or require cryogenic conditions. By constructing a high-fidelity approximation of a single-photon state with phase-averaged coherent states, we observe the normalized second-order intensity correlation dips significantly below the classical limit of 0.5. The method allows for tunable noise suppression via optimization of the state representation. Our results establish the feasibility of using conditionally prepared classical states to simulate quantum interference phenomena in the radio-frequency domain. This technique opens the door to realizing other quantum protocols, such as Bell inequality tests, in frequency ranges where standard quantum technologies are currently infeasible.

Figures (3)

• Figure 1: (a) Schematic outline of the HOM interference experiment. (b) Photograph of the actual experimental setup. (c) Block-scheme of the setup.
• Figure 2: (a) Illustration of partially overlapping radio pulses of the same amplitude, which were used in the experiment. (b) An illustration of the completely overlapping radio pulses after the beam-splitter. (c) An illustration of the HOM dip for the interference of identical phase-averaged coherent states carried by rectangular radio pulses. The dip is shown versus the relative time-shift of the pulses expressed as the percentage of the pulse width. (d) HOM dips obtained for the realistic pairs of radio pulses of the same shape and different amplitudes proportional to the respective voltages shown in the left inset; the right inset shows the signal-to-noise ratio (SNR) for the corresponding HOM curves. Notice that for the curves corresponding to $\alpha=0.4$, $\alpha=0.8$, and $\alpha=1.45$ the SNR exceeds 25 dB and these three curves are almost completely overlapping.
• Figure 3: (a,b) The HOM dip for the set of amplitudes shown for Fig. \ref{['fig2']}(d) and the coefficients $c_j$ shown in the corresponding insets.