Quantum-enhanced biosensing enables earlier detection of bacterial growth

TL;DR

This work tackles the sensitivity-speed trade-off in optical detection of bacterial growth by applying quantum-enhanced photometry with squeezed light to absorbance measurements of $E. coli$ MG1655. A three-module photometer integrates a squeezed-light source delivering squeezing of $-6.19$ dB at $1064$ nm, a displacement stage, and a real-time detector; the readout operates at $1.7$ mW while maintaining low noise. Using a truncated Gaussian model for absorbance and a binary hypothesis test between $H_0$ (no growth) and $H_1$ (growth), the study shows growth onset can be identified approximately $30$ minutes earlier than with a classical sensor while keeping false-alarm rates comparable. The result demonstrates a practical quantum advantage for real-time, low-photodamage biosensing and points toward scalable quantum-enabled diagnostics.

Abstract

Rapid detection of bacterial growth is crucial in clinical, food safety, and environmental contexts, yet conventional optical methods are limited by noise and require hours of incubation. Here, we present the first experimental demonstration of a quantum-enhanced photometric measurement for early bacterial detection using squeezed light. By monitoring the optical absorbance of an Escherichia coli culture with a quantum probe, we achieve a sensitivity beyond the shot-noise limit, enabling identification of growth onset up to 30 minutes earlier than with a classical sensor. The noise reduction is validated through statistical modeling with a truncated Gaussian distribution and hypothesis testing, confirming earlier detection with low false-alarm rates. This work illustrates how quantum resources can improve real-time, non-invasive diagnostics. Our results pave the way for quantum-enhanced biosensors that accelerate detection of microbial growth and other biological processes without increasing photodamage.

Figures (12)

• Figure 1: Experimental setup. The system contains three main parts: 1) Squeezed light source, 2) Displacement beam module, and 3) Photometer. OPA: Optical Parametric Amplifier, DM: Dichroich mirror, OI: Optical isolator, HWP: Half-wave plate, PBS: Polarizing beam-splitter, BS: Beam-splitter, PD: Photodetector, EOAM: Electro-optic modulator, AOM: Acoustic optical modulator.
• Figure 2: Measurement dataset: red dots indicate the squeezed state and blue dots the coherent state of light. (a) Normalized mean value (in arbitrary units) as a function of time (hours). (b) Variance of the squeezed and coherent states, normalized to the shot-noise level and expressed in dB. The purple dashed curve shows the expected squeezing level based on losses inferred from the growth curve.
• Figure 3: Probability density function. Growth curve of E. coli in terms of absorbance versus growth time (hours). The data are fitted with a Gompertz function given by Eq. (2). The red and blue curves represent the mode of the truncated distribution for measurements performed with squeezed and coherent states of light, respectively.
• Figure 4: Transmissivity as a function of growth time (hours). In both panels, the constant curve corresponds to the transmissivity of the blank measurement, while the polynomial curve represents the growth process. (a) Coherent-state measurements are shown in blue. (b) Squeezed-state measurements are shown in red. In both cases, the growth curve becomes distinguishable from the blank approximately half an hour earlier when using squeezed states of light.
• Figure 5: (a) Mean error probability as a function of growth time (hours). (b) False-negative probability as a function of growth time (hours). Red curves represent measurements performed using squeezed states of light; blue curves correspond to measurements using coherent states.