Quantum Mechanics is the theory that governs the very small, including individual particles of light called photons. A pair of photons can coordinate in certain ways, such that measuring each of them tends to give the same result under some conditions and opposite results under others. This high level of coordination that photons can exhibit, which cannot be simulated by classical (non-quantum) means, is called entanglement. In addition to being of great fundamental importance, this coordination forms the basis for the emerging technologies of quantum cryptography and quantum computing, so it is important to probe for any limits of this coordination in the most extreme conditions over (literally) astronomical distances. This project will use the hardware developed by the principal investigator for earlier quantum tests to record the time of arrival of individual photons from pulsars, which are fast-spinning neutron stars with extremely strong magnetic fields that produce beams of radiation across the electromagnetic spectrum. Careful measurements will shed light on various models behind pulsar emission and provide measurements of certain aspects of Einstein’s General relativity. All of these experiments involve building custom electronics with undergraduates, and as part of this project, the principal investigator will modernize the way the electronics lab course is taught to the college’s science majors. Rather than passively analyzing, building, debugging, and recording results from standard circuits, students will take an active role in design each week. This role will start with small, well-defined design tasks, but will deliberately scale up to an open-ended final project. Many research groups would benefit from new or improved instrumentation, and small instrumentation projects solicited from researchers across the science departments will form the core of the list of suggested final projects.
It is very important in performing tests of Bell’s Inequality on quantum-mechanically entangled particles to choose the measurement basis for each particle in a way that cannot be predicted or influenced by the source of entangled particles or by the other particle. The principal investigator’s unique contribution to the field has been to improve tests of Bell’s Inequality using astronomical sources: both stars in our own galaxy and quasars at the heart of distant galaxies that emitted their light when the universe was only a tenth as old as it is today. This project continues to use quasars as a source of measurement settings whose sequence cannot be predicted without having access to the past lightcones of those quasars. This will improve delayed-choice experiments and tests of quantum erasure, reducing the plausibility that locally-causal schemes can explain the observed phenomena. This project involves building a Sagnac interferometer as a bright and pure source of entangled photons. The quality of the resulting entanglement will be measured and optimized in real time with a novel dual rotating waveplate technique. This entanglement source will be brought to an astronomical observatory and used to perform a version of Wheeler’s delayed-choice experiment where information coming from a distant quasar effectively inserts or removes a beam splitter. It will also be used as part of a test of quantum erasure, where the decision to erase or not erase which-path information will be determined not locally, but by light from a distant quasar. Both of these experiments would put constraints on locally-causal explanations for the observed quantum phenomena. The same quasar-recording hardware will be used to do time-resolved polarimetry and coarse spectral binning with sub-nanosecond precision. Similar to the principal investigator’s work on the Crab pulsar, this improved device will set limits on Einstein’s Weak Equivalence Principle by constraining the difference in arrival times between photons of different energies and polarizations.
This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
