Researchers at the Technion, Israel Institute of Technology, report a first in ultrafast quantum optics: a single-shot measurement of the spectral phase and amplitude of individual bright squeezed vacuum (BSV) pulses, enabling reconstruction of each pulse’s temporal profile without averaging. The achievement, which relied on a spectral-interferometry technique and a coherent reference pulse, addresses a long-standing challenge in quantum optics: how to characterize, in real time, light pulses that fluctuate strongly from one shot to the next and can carry extremely large numbers of photons.
What Bright Squeezed Vacuum Actually Is
BSV is a form of quantum light generated when a pump laser passes through a traveling-wave optical parametric amplifier. Unlike ordinary laser light, BSV has no stable average electric field. Instead, its energy comes entirely from quantum fluctuations, amplified to macroscopic intensity. Those fluctuations can produce pulses containing, according to the Technion’s institutional bibliography, up to roughly 10^13 photons per pulse. A separate account from the same institution describes the figure as up to one trillion photons; the two descriptions are not identical, but both convey that the pulses can contain on the order of a trillion photons.
That enormous photon count, combined with shot-to-shot randomness in both duration and shape, is exactly what made BSV so difficult to measure. Classical ultrafast diagnostics average over many pulses, which works fine when each pulse looks roughly the same. BSV pulses do not. Each one is a unique quantum event, and averaging destroys the very information physicists want to extract.
How the Technion Team Solved the Problem
The Technion group’s method uses single-shot spectral interferometry. A known coherent reference pulse is combined with the unknown BSV pulse, and the two interfere on a spectrometer. “By recording the resulting interference patterns, the real-time characteristics of the laser pulse can be reconstructed,” according to the Technion’s official account of the work. Because the reference pulse is well characterized, the spectral phase and amplitude of the BSV pulse can be extracted from a single interferogram, with no need to repeat the measurement or average across shots.
The technique was applied to BSV pulses generated at 1040 nm. According to the team’s preprint on arXiv, the measured average pulse duration was 27.2 femtoseconds, with a shot-to-shot standard deviation of 5.5 femtoseconds. That 5.5 fs variation is itself a significant finding: it provides a direct, shot-by-shot measure of how much BSV pulses differ from one another in the time domain. An earlier seminar listing from the Technion physics faculty had cited an indicative pulse-duration scale of roughly 40 fs. The preprint’s tighter figure of 27.2 fs may reflect differences in experimental conditions and/or how the duration was estimated in each context, though both values fall in the tens-of-femtoseconds regime expected for broadband parametric sources.
Why Previous Methods Fell Short
Ultrafast pulse characterization is a mature field for classical light. Techniques such as FROG (frequency-resolved optical gating) and SPIDER (spectral phase interferometry for direct electric-field reconstruction) have been standard tools for decades. But these methods generally assume repeatable pulses or require multiple acquisitions. For highly fluctuating sources like supercontinuum generation, single-shot temporal measurement of individual pulses has remained out of reach, as Georgia Tech’s FROG group has noted.
On the quantum side, electro-optic sampling (EOS) has emerged as a way to probe the electric-field operator of quantum light, including multimode squeezed states. A separate theoretical framework published on arXiv describes how EOS can reconstruct quantum field statistics for ultrabroadband Gaussian states. And prior experimental work has demonstrated electro-optic shearing interferometry for characterizing the temporal and spectral mode structure of single photons. But single photons and BSV occupy opposite ends of the intensity spectrum. BSV’s extreme photon numbers and chaotic pulse shapes demanded a different strategy, one that could handle macroscopic energy levels while still resolving quantum-scale temporal features.
Measuring Quantum Uncertainty in Real Time
The Technion result sits alongside a broader push to pin down quantum behavior on ultrafast timescales. Scientists at the University of Arizona reported in October 2025 the first-ever measurement of quantum uncertainty in real time, a parallel but distinct achievement focused on tracking how uncertainty itself evolves during light-matter interactions. Together, these results signal that the field is moving from statistical descriptions of quantum light, built from many repeated measurements, toward direct, shot-by-shot observation of quantum dynamics as they happen.
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*This article was researched with the help of AI, with human editors creating the final content.
