[Paper Review] Highly multimode visible squeezed light with programmable spectral correlations through broadband up-conversion

Federico Presutti, Logan G. Wright+5 more|arXiv (Cornell University)|Jan 11, 2024

Photorefractive and Nonlinear Optics4 citations

TL;DR

This paper demonstrates the generation of highly multimode visible squeezed light—over 400 frequency modes with ~700 photons per shot—using broadband adiabatic frequency conversion (AFC) to shift infrared-squeezed states to the visible spectrum while programmably shaping their spectral correlations. The method enables efficient, high-fidelity measurement with a single EMCCD camera, offering a compact, low-resource path to scalable frequency-encoded quantum information processing.

ABSTRACT

Multimode squeezed states of light have been proposed as a resource for achieving quantum advantage in computing and sensing. Recent experiments that demonstrate multimode Gaussian states to this end have most commonly opted for spatial or temporal modes, whereas a complete system based on frequency modes has yet to be realized. Instead, we show how to use the frequency modes simultaneously squeezed in a conventional, single-spatial-mode, optical parametric amplifier when pumped by ultrashort pulses. Specifically, we show how adiabatic frequency conversion can be used not only to convert the quantum state from infrared to visible wavelengths, but to concurrently manipulate the joint spectrum. This near unity-efficiency quantum frequency conversion, over a bandwidth >45 THz and, to our knowledge, the broadest to date, allows us to measure the state with an electron-multiplying CCD (EMCCD) camera-based spectrometer, at non-cryogenic temperatures. We demonstrate the squeezing of >400 frequency modes, with a mean of approximately 700 visible photons per shot. Our work shows how many-mode quantum states of light can be generated, manipulated, and measured with efficient use of hardware resources -- in our case, using one pulsed laser, two nonlinear crystals, and one camera. This ability to produce, with modest hardware resources, large multimode squeezed states with partial programmability motivates the use of frequency encoding for photonics-based quantum information processing.

Motivation & Objective

• To realize a fully frequency-mode-based continuous-variable quantum system using multimode squeezed light.
• To overcome the challenge of detecting and manipulating high-bandwidth, multimode quantum states in the visible spectrum.
• To demonstrate efficient, high-throughput quantum frequency conversion that preserves and controls spectral correlations.
• To enable practical, low-resource implementation of large-scale multimode Gaussian quantum states using one laser, two crystals, and a single camera.

Proposed method

• Use a degenerate optical parametric amplifier (DOPA) to generate highly multimode squeezed vacuum in the near-infrared at 1550 nm.
• Apply broadband adiabatic frequency conversion (AFC) using a 1033 nm pump to convert the squeezed state to visible wavelengths (620 nm), preserving quantum correlations.
• Control the joint spectral structure of the output by shaping the pump’s spectro-temporal profile, enabling programmable spectral correlations.
• Measure the final state using a frequency-resolved electron-multiplying CCD (EMCCD) camera, which detects photon counts in discrete frequency bins.
• Model the system using linear unitary transformations and covariance matrices to describe the quantum state evolution from infrared to visible modes.
• Validate the experimental results against classical simulability bounds using detector efficiency and dark count rate parameters to assess quantum advantage potential.

Figure 4: Preparing the joint spectrum via frequency conversion. By pulse shaping the AFC pump $A(\omega_{\text{p}})$ , we can modify the linear unitary transformation $U$ performed by the AFC process, hence the state and the measured spectral photon-number correlations. The pump spectral intensity

Experimental results

Research questions

• RQ1 Can highly multimode visible squeezed light be generated with programmable spectral correlations using broadband frequency conversion?
• RQ2 To what extent can adiabatic frequency conversion preserve and control the entanglement structure of multimode squeezed states?
• RQ3 Can EMCCD-based frequency-resolved photon counting enable high-fidelity, high-throughput measurement of large multimode quantum states at non-cryogenic temperatures?
• RQ4 How does pump bandwidth affect the connectivity and entanglement structure of the converted multimode state?
• RQ5 What is the practical limit of quantum advantage in Gaussian boson sampling when using EMCCD cameras with realistic detector parameters?

Key findings

• The experiment achieved the generation of over 400 frequency modes of visible squeezed light, with a mean photon number of approximately 700 per shot.
• Broadband adiabatic frequency conversion was demonstrated with a conversion bandwidth exceeding 45 THz, the broadest to date.
• The method enabled full control over spectral correlations via pump shaping, allowing programmable manipulation of the joint spectrum.
• The use of a single EMCCD camera enabled frequency-resolved photon counting at room temperature, avoiding cryogenic cooling.
• Simulations showed that pump bandwidth directly influences entanglement connectivity, with broader pumps enabling more complex entanglement structures.
• The experimental setup remains outside the classically simulable regime when using realistic EMCCD parameters, supporting the potential for quantum advantage in Gaussian boson sampling.

Figure A5: Photographs of the Experiment. The beam paths are overlaid. Beam color to wavelength legend: H TML]00CCCC 1550 H TML]996185 1033 H TML]AE4132 775 H TML]FFA500 620 H TML]82B366 516 nm. a. Pulse shaper. b. DOPA. c. AFC. d. Spectrometer. e. 775 nm pump generation. f. Monochromation and coinc