Quantum optics
Can a chip change the colour of single photons without loss?
Open access · cc by · source: Europe PMC
An on-chip lithium niobate modulator shifted single photons' frequency by up to about 641 GHz and squeezed their bandwidth 18-fold, without adding noticeable loss or noise.
Study at a glance
- Design
- Other — Lab experiment: heralded single photons from down-conversion were phase-modulated by a double-pass thin-film lithium niobate modulator for spectral shearing and time-lens compression, with spectra and two-photon interference measured.
- N
- No sample count; a single integrated modulator device characterised in several configurations.
- Population
- Telecom-band (~1560 nm) heralded single-photon pulses and one double-pass thin-film lithium niobate phase modulator
- Outcome
- Single-photon frequency shift, spectral bandwidth after compression, and Hong-Ou-Mandel interference visibility
Structured fields used in claim comparison tables when every cited study has a complete layer.
Key findings
Frequency shifts reached ±641 GHz (±5.2 nm), about three times larger than earlier bulk-modulator demonstrations, with no added insertion loss beyond coupling drift. Two photons initially 154 GHz apart interfered with only 23.1% visibility, but after shifting one of them the visibility rose to 90.5%. Used as a time lens, the modulator compressed a photon's bandwidth from 807 GHz to 43.1 GHz, a factor of 18.7.
Methodology
The authors made pairs of photons near 1560 nm by spontaneous parametric down-conversion and sent one photon through a thin-film lithium niobate phase modulator whose waveguide passes the microwave electrode twice. Timing the photon to the steep slope of the sinusoidal microwave drive produced a linear phase ramp (spectral shearing), while timing it to the drive's trough gave a quadratic phase that acts as a time lens. They measured single-photon spectra by dispersive time-of-flight and tested whether shifted photons stayed indistinguishable using Hong-Ou-Mandel interference.
Limitations
Only one device was tested, and its low half-wave voltage occurs only at specific drive frequencies because of the double-pass loopback, so it is not a broadband modulator. Timing jitter between laser and microwave drive broadened the shifted spectra, and the quoted interference visibilities are background-subtracted (raw values were lower). The bulk waveshaper used for dispersion was off-chip, and the method has not been shown for narrowband photons from quantum emitters or as a partial frequency beam splitter.
How this study connects
Role on claims
Each row is a claim on a concept or method page where this paper supports, challenges, or qualifies the statement. Roles are hand-checked — not a model guess.
Quantum interfaces can match photons from different sources.
Photons can be converted between colours and modes while keeping quantum properties: a thin-film lithium niobate modulator shifted photons by ±641 GHz, raising two-photon interference from 23.1% to 90.5%, and sum-frequency conversion kept OAM photons nonclassical with process fidelities near 0.95.
Evidence for the claim as stated.
Reported visibilities differ in processing: some are background-subtracted (lithium niobate shifter) while others are raw (microring Franson visibilities), so numbers are not directly comparable.
Evidence for the claim as stated.
Open questions
Tensions this paper is part of
From concept pages' “where studies disagree.” Disagreement means the same question; scope means different assays, populations, or outcomes.
Reported visibilities differ in processing: some are background-subtracted (lithium niobate shifter) while others are raw (microring Franson visibilities), so numbers are not directly comparable.
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