arXiv subjects

Tomas Lamich

Publications and source records attributed to Tomas Lamich.

3 recordsLinked to original sources

arXiv2025

Detection of photon-level signals embedded in sunlight with an atomic photodetector

The detection of few-photon signals in a broadband background is an extreme challenge for photon counting, requiring filtering that accepts a narrow range of optical frequencies while strongly rejecting all others. Recent work [Zarraoa et. al, Phys. Rev. Res. 6, 033338 (2024)] demonstrated that trapped single atoms can act as low dark-count narrow-band photodetectors. Here we show that this ``quantum jump photodetector'' (QJPD) approach can also detect photon-level signals embedded in strong sunlight. Using a single rubidium atom as a QJPD, we count arrivals of individual narrow-band laser photons embedded in sunlight powers of order $10^{10}$ photons/s. We derive a rate-equation model for the atom's internal-state dynamics in sunlight, and find quantitative agreement with experiment. Using this model, we calculate the channel capacity over a noisy communication channel when sending weak coherent states and detecting them in the presence of sunlight, achieving a representative rate of 0.5 bits per symbol when sending 150 probe photons per 10 ms time-bin, embedded in 1 nW of sunlight (of order $10^{10}$ photons/s in the visible and near-infrared bands). The demonstration may benefit background-limited applications such as daytime light detection and ranging (LIDAR), remote magnetometry, and free-space classical and quantum optical communications.

quant-ph↗

arXiv2024

Quantum jump photodetector for narrowband photon counting with a single atom

Using a single neutral 87Rb atom held in an optical trap, and "quantum jump" detection of single-photon-initiated state changes, we demonstrate a single-photon quantum jump photodetector (QJPD) with intrinsically narrow bandwidth and strong rejection of out-of-band photons, of interest for detecting weak optical signals in the presence of a strong broadband background. By analyzing fluorescence photon count distributions for the bright and dark states with and without excitation, we measure quantum efficiency of 2.9(2)$\times 10^{-3}$, a record for single-pass quantum jump production, and signal-photon-unprovoked "dark jump" rate - analogous to the dark count rate of other detectors - 3(10)$\times 10^{-3}$ jumps per second during passive accumulation plus 4.0(4)$\times 10^{-3}$ jumps per readout, orders of magnitude below those of traditional single-photon detectors. Available methods can substantially improve QJPD quantum efficiency, dark jump rate, bandwidth and tunability.

quant-ph↗

arXiv2024

Precise, super-resolving intensity measurement by quantum jump spectroscopy of a single neutral atom

We present precise, sub-wavelength optical intensity measurement using a single trapped $^{87}$Rb atom as a sensor. The intensity is measured by the scalar ac Stark shift it produces on the $F=1 \rightarrow F'=2$ hyperfine transition of the D$_{2}$ line, chosen for its $F' = F+1$ structure and very small tensor polarizability. To boost signal and reduce measurement-induced perturbations, we use a quantum jump spectroscopy technique in which a single absorbed photon on a transition of interest induces the scattering of hundreds of photons on a bright closed transition. The method greatly reduces systematic effects associated with the atomic state, optical polarization, probe power, and atom heating, and gives the atomic temperature as a second spectroscopic observable. We demonstrate the method by measuring the intensity at the focus of an optical tweezer.

physics.atom-ph↗