Amy Brown | Searcharxiv

arXiv2018

Astronomical random numbers for quantum foundations experiments

Photons from distant astronomical sources can be used as a classical source of randomness to improve fundamental tests of quantum nonlocality, wave-particle duality, and local realism through Bell's inequality and delayed-choice quantum eraser tests inspired by Wheeler's cosmic-scale Mach-Zehnder interferometer gedankenexperiment. Such sources of random numbers may also be useful for information-theoretic applications such as key distribution for quantum cryptography. Building on the design of an "astronomical random-number generator" developed for the recent "cosmic Bell" experiment [Handsteiner et al., Phys. Rev. Lett. 118, 060401 (2017)], in this paper we report on the design and characterization of a device that, with 20-nanosecond latency, outputs a bit based on whether the wavelength of an incoming photon is greater than or less than 700 nm. Using the one-meter telescope at the Jet Propulsion Laboratory (JPL) Table Mountain Observatory, we generated random bits from astronomical photons in both color channels from 50 stars of varying color and magnitude, and from 12 quasars with redshifts up to $z = 3.9$. With stars, we achieved bit rates of $\sim 1 \times 10^6$ Hz / m$^2$, limited by saturation for our single-photon detectors, and with quasars of magnitudes between 12.9 and 16, we achieved rates between $\sim 10^2$ and $2 \times 10^3$ Hz /m$^2$. For bright quasars, the resulting bitstreams exhibit sufficiently low amounts of statistical predictability as quantified by the mutual information. In addition, a sufficiently high fraction of bits generated are of true astronomical origin in order to address both the locality and freedom-of-choice loopholes when used to set the measurement settings in a test of the Bell-CHSH inequality.

quant-ph↗

arXiv2018

Testing the Weak Equivalence Principle using Optical and Near-Infrared Crab Pulses

The Weak Equivalence Principle states that the geodesics of a test particle in a gravitational field are independent of the particle's constitution. To constrain violations of the Weak Equivalence Principle, we use the one-meter telescope at Table Mountain Observatory near Los Angeles to monitor the relative arrival times of pulses from the Crab Pulsar in the optical ($λ\approx 585$ nm) and near-infrared ($λ\approx 814$ nm) using an instrument which detects single photons with nanosecond-timing resolution in those two bands. The infrared pulse arrives slightly before the visible pulse. Our three analysis methods give delays with statistical errors of $Δt_{obs} = 7.41 \pm 0.58$, $0.4 \pm 3.6$, and $7.35 \pm 4.48$ microseconds (at most 1/4000 of the pulsar period). We attribute this discrepancy to systematic error from the fact that the visible and infrared pulses have slightly different shapes. Whether this delay emerges from the pulsar, is caused by passing through wavelength-dependent media, or is caused by a violation of the equivalence principle, unless there is a fine-tuned cancellation among these, we set the first upper limit on the differential post-Newtonian parameter at these wavelengths of $Δγ< 1.07 \times 10^{-10}~(3σ)$. This result falls in an unexplored region of parameter space and complements existing limits on equivalence-principle violation from fast radio bursts, gamma ray bursts, as well as previous limits from the Crab.

astro-ph.HE↗