Quantum matched filtering: breaking time-energy separability by 12 orders of magnitude

• URL: http://arxiv.org/abs/2503.03583v3
• Date: Sun, 26 Oct 2025 03:58:26 GMT
• Title: Quantum matched filtering: breaking time-energy separability by 12 orders of magnitude
• Authors: Nir Nechushtan, Hanzhong Zhang, Yosef London, Mallachi Meller, Haia Amichai, Eliahu Cohen, Avi Pe'er,
• Abstract summary: Time-energy entangled photons can be simultaneously correlated in time difference and frequency sum with no minimum limit.<n>We create biphotons with extreme time-energy entanglement and measure a relative uncertainty of time-difference and frequency-sum that violates the classical separability bound by >12 orders of magnitude.<n>Our experiment and supporting theory pave the way for quantum sensing applications, such as quantum illumination (radar)
• Score: 0.6156528407876973
• License: http://creativecommons.org/licenses/by/4.0/
• Abstract: Detection of signals buried in noise is the major challenge for sensing. Classically, the optimal detector is a matched filter, whose sensitivity meets the classical limit of correlation between the filter target and the measured signal within the noise. For classical signals, the correlation is limited by the separability criterion in frequency-time. Quantum states, however are not necessarily separable, and the correlation between entangled particles can surpass the classical limits. Specifically, time-energy entangled photons can be simultaneously correlated in time difference and frequency sum with no minimum limit, potentially leading to a drastic enhancement of sensitivity for diversified sensing applications. Yet, to enjoy this quantum enhancement, a unique, global detector is needed that can recover the complete information of entanglement in a single shot, i.e. measure the combined correlated variables of time-difference and frequency-sum without measuring the individual frequencies or times. Such a global measurement could, in principle, be realized using the reverse disentangling interaction, such as sum-frequency generation (SFG), but nonlinear interactions at the single-photon level have long been prohibitively inefficient, significantly restricting practical implementations. Here we overcome this barrier: We measure simultaneously and efficiently both the frequency-sum (SFG spectrum) and the time-difference (relative group delay/dispersion) by stimulating the SFG recombination with a strong pump. We generate biphotons with extreme time-energy entanglement (octave-spanning spectrum of 113THz) and measure a relative uncertainty of time-difference and frequency-sum that violates the classical separability bound by >12 orders of magnitude. Our experiment and supporting theory pave the way for quantum sensing applications, such as quantum illumination (radar).

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