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arxiv: 2508.08857 · v1 · submitted 2025-08-12 · ⚛️ physics.optics · quant-ph

A Broadband Squeezed Light Source for Table-Top Interferometry

Fabio Bergamin , Nikitha Kuntimaddi , Abhinav Patra , Stephanie Montoya , Moritz Mehmet , Katherine Dooley , Hartmut Grote , Henning Vahlbruch This is my paper

Pith reviewed 2026-05-18 23:01 UTC · model grok-4.3

classification ⚛️ physics.optics quant-ph
keywords squeezed lightoptical parametric amplifierbalanced homodyne detectionquantum noise reductiontable-top interferometrybroadband squeezingshot noise limitedspace-time fluctuations
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The pith

A hemilithic OPA generates up to 6.8 dB of squeezed light across a 100 MHz bandwidth for table-top interferometry.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper shows that a compact squeezed light source built around a hemilithic optical parametric amplifier can deliver substantial quantum noise reduction over a wide frequency band. Direct balanced homodyne measurements confirm peak squeezing of 6.8 dB and at least 3 dB sustained across the full 100 MHz range, rising to an inferred 8.6 dB once dark noise is subtracted. This source is developed specifically for the QUEST experiment's co-located table-top Michelson interferometers, which target shot-noise limited operation between 1 and 200 MHz to search for stationary space-time fluctuations. A reader would care because achieving this level of squeezing in a stable, long-term device could lower the noise floor enough to make faint fluctuations detectable in a laboratory-scale setup rather than requiring kilometer-scale facilities.

Core claim

The central claim is that a hemilithic optical parametric amplifier with a 43.6 mm round-trip optical length and 138 MHz linewidth produces broadband squeezed light suitable for long-term table-top use. Balanced homodyne detection directly records up to 6.8 dB of squeezing while maintaining at least 3 dB across the entire 100 MHz measurement bandwidth. After subtracting the dark noise contribution the inferred squeezing reaches 8.6 dB, establishing the device as the broadest-linewidth squeezed source reported for stable operation.

What carries the argument

The hemilithic optical parametric amplifier, a short-cavity nonlinear resonator that sets both the broad 138 MHz linewidth and the stable operating conditions required for continuous interferometer use.

If this is right

  • The QUEST interferometers can reach shot-noise reduction of 6 dB inside the OPA linewidth while remaining shot-noise limited from 1 to 200 MHz.
  • The 100 MHz bandwidth fully covers the frequency range needed to probe stationary space-time fluctuations in the table-top setup.
  • The source supports continuous, stable operation without frequent realignment, enabling extended data runs.
  • Balanced homodyne characterization provides an independent verification of squeezing that can be compared with interferometer output.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • Compact OPA designs of this type could be adapted for other table-top quantum sensors that need broadband noise reduction beyond the QUEST application.
  • Performance inside the full power-recycled Michelson system may reveal integration effects not visible in the isolated source characterization.
  • Further shortening the cavity could push the linewidth higher while preserving long-term stability for even wider-bandwidth experiments.

Load-bearing premise

Subtracting the dark noise spectrum from the measured homodyne data yields an accurate inference of the true squeezing level without systematic overestimation from unaccounted losses or drifts.

What would settle it

A direct squeezing measurement performed after injecting the source into the operational QUEST interferometers that shows sustained levels falling below 3 dB across the 100 MHz band due to additional losses or instability.

Figures

Figures reproduced from arXiv: 2508.08857 by Abhinav Patra, Fabio Bergamin, Hartmut Grote, Henning Vahlbruch, Katherine Dooley, Moritz Mehmet, Nikitha Kuntimaddi, Stephanie Montoya.

Figure 1
Figure 1. Figure 1: Summary of previous results. As shown in the plot, the SLS characterised in this work has [PITH_FULL_IMAGE:figures/full_fig_p003_1.png] view at source ↗
Figure 2
Figure 2. Figure 2: Layout of the SLS and of the BHD, including the control loops. BS: 50:50 beam splitter, [PITH_FULL_IMAGE:figures/full_fig_p004_2.png] view at source ↗
Figure 3
Figure 3. Figure 3: BHD signals measured with the spectrum analyser using an RBW of 1 MHz and averaging [PITH_FULL_IMAGE:figures/full_fig_p006_3.png] view at source ↗
Figure 4
Figure 4. Figure 4: Spectrogram of the BHD signal recorded during a one-hour continuous lock. A beam [PITH_FULL_IMAGE:figures/full_fig_p007_4.png] view at source ↗
Figure 5
Figure 5. Figure 5: Normalised quantum noise spectra. Both cases—with and without dark noise sub [PITH_FULL_IMAGE:figures/full_fig_p009_5.png] view at source ↗
read the original abstract

We report on the characterisation of one of two broadband squeezed light sources developed for the Quantum Enhanced Space-Time (QUEST) experiment, using balanced homodyne detection. QUEST consists of a pair of co-located, table-top, power-recycled Michelson interferometers designed to probe stationary space-time fluctuations. The interferometers are designed to be shot-noise limited in the frequency range from 1 to 200 MHz, and squeezed light will be employed with the goal to reduce the shot noise by 6 dB at frequencies inside the linewidth of the optical parametric amplifier (OPA). We directly observed up to 6.8 dB of squeezing and maintained at least 3 dB of squeezing across the full 100 MHz measurement bandwidth. After accounting for the dark noise contribution, the inferred squeezing level increased to 8.6 dB. Our squeezed light source is based on a hemilithic OPA with a 43.6 mm round-trip optical length and a linewidth of 138 MHz, making it the broadest-linewidth device to date among those suitable for long-term operation.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

1 major / 2 minor

Summary. The manuscript reports the experimental characterization of a hemilithic optical parametric amplifier (OPA) as a broadband squeezed-light source for the QUEST table-top interferometers. Using balanced homodyne detection, the authors claim direct observation of up to 6.8 dB squeezing with at least 3 dB maintained across the full 100 MHz measurement bandwidth; after dark-noise subtraction the inferred squeezing reaches 8.6 dB. The device has a 43.6 mm round-trip length and 138 MHz linewidth, presented as the broadest such source suitable for long-term operation, with the goal of delivering 6 dB shot-noise reduction inside the OPA linewidth for the 1–200 MHz band.

Significance. If the reported performance is confirmed, the work supplies a practical, high-bandwidth squeezed-light source directly applicable to table-top Michelson interferometers targeting stationary space-time fluctuations. The explicit separation of observed versus inferred squeezing levels and the direct homodyne data constitute a clear experimental contribution; the 138 MHz linewidth claim, if substantiated, would be a useful benchmark for similar devices.

major comments (1)
  1. [Results on squeezing characterization and dark noise subtraction] The inference of 8.6 dB squeezing after dark-noise subtraction (abstract and results section on homodyne spectra) is load-bearing for the claim that the source meets the 6 dB shot-noise reduction target. The manuscript must explicitly verify that dark noise was recorded under identical local-oscillator power, electronic gain, and frequency response as the signal traces; any unaccounted mismatch or correlation would systematically overestimate the delivered squeezing and weaken the performance guarantee for QUEST.
minor comments (2)
  1. [Abstract] The abstract states the squeezing values without accompanying uncertainties or error bars; inclusion of statistical and systematic uncertainties on the 6.8 dB, 3 dB, and 8.6 dB figures would improve clarity.
  2. [Discussion or experimental methods] Long-term stability data (drift of squeezing level over hours or days) are referenced only qualitatively; a brief time-series measurement or Allan deviation would directly support the “long-term operation” suitability claim.

Simulated Author's Rebuttal

1 responses · 0 unresolved

We thank the referee for their constructive review and positive assessment of the work. We address the major comment below and have revised the manuscript to incorporate the requested clarification.

read point-by-point responses

  1. Referee: The inference of 8.6 dB squeezing after dark-noise subtraction (abstract and results section on homodyne spectra) is load-bearing for the claim that the source meets the 6 dB shot-noise reduction target. The manuscript must explicitly verify that dark noise was recorded under identical local-oscillator power, electronic gain, and frequency response as the signal traces; any unaccounted mismatch or correlation would systematically overestimate the delivered squeezing and weaken the performance guarantee for QUEST.

    Authors: We agree that explicit verification of the dark-noise acquisition conditions is essential to support the inferred squeezing levels. In the revised manuscript we have added a dedicated paragraph in the Homodyne Detection section stating that dark-noise spectra were acquired with the local oscillator blocked but with identical electronic gain, frequency response, and acquisition settings as the signal traces. The dark-noise measurement was performed immediately before and after each squeezing spectrum to minimize any temporal drift. We have also included a supplementary figure overlaying the raw, dark-noise-subtracted, and shot-noise traces to allow direct assessment of the correction. These changes ensure the 8.6 dB inferred value is presented with full experimental transparency. revision: yes

Circularity Check

0 steps flagged

No circularity: pure experimental characterization with no derivations or self-referential claims

full rationale

This paper reports direct experimental measurements of squeezing in a hemilithic OPA using balanced homodyne detection. Observed squeezing reaches 6.8 dB with at least 3 dB across 100 MHz, and an inferred 8.6 dB after standard dark-noise subtraction. The linewidth of 138 MHz is stated from the device parameters and data. No theoretical derivation chain, fitted parameters renamed as predictions, self-citations as load-bearing uniqueness theorems, or ansatzes exist. All claims reduce to empirical spectra and device specifications without reducing to their own inputs by construction. The analysis is self-contained against external benchmarks.

Axiom & Free-Parameter Ledger

0 free parameters · 0 axioms · 0 invented entities

This is an experimental device characterization with no theoretical derivation; the ledger contains no free parameters, axioms, or invented entities.

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