Table Top Experiments PI Meeting

Sougato Bose
University College London

Quantum Nature of Gravity via Quantum Technologies: Gravitational Entanglement
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I will discuss a scheme to test the nonclassical behavior of gravity in the laboratory. As a precursor, a method for matter wave interferometry with large objects, namely the Stern-Gerlach interferometer, will be discussed. We will then discuss how gravitational entanglement generation between two matter wave interferometers formed of large objects can be tested by measuring spins. The justification of this approach in proving the quantum nature of gravity will be described. In this context, the principal practical challenges and potential mitigation methods will also be described.
 

David DeMille
Johns Hopkins University

Electric Dipole Moments: Powerful Probes for New Physics

An electric dipole moment (EDM) along the spin axis of any quantized particle requires violation of time-reversal (T) symmetry. While T symmetry is broken in the Standard Model (SM), certain symmetries of the SM dramatically suppress the size of EDMs—but most extensions to the standard model lack a mechanism to suppress T symmetry violation. In these models, EDMs arise due to virtual exchange of new particles, beyond those in the SM. The effect of these new particles is generically proportional to the inverse square of their mass. Current experiments are already sensitive enough to probe for certain new particles with mass in the 5-50 TeV range, far beyond the direct reach of the Large Hadron Collider.

Over the past decade, remarkably fast progress has been made in the search for the electron EDM, by exploiting the large electric fields inside polar molecules to amplify the energy shift due to the EDM. New technologies for control of polar molecules—such as laser cooling, assembly from ultracold atoms, production of radioactive molecules, and optical readout of spins embedded in crystals—have emerged. With these, the recent rapid rate of progress seems poised to continue, and also to extend to searches for effects analogous to the EDM in nuclei. These experiments promise to probe new T- violating physics at energy scales over 1 PeV. They also can serve as sensitive detectors for dark matter axions with low mass.
 

Gurudev Dutt
University of Pittsburgh

Toward macroscopic quantum superpositions with magnetically levitated diamond crystals
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We report progress on a new platform for probing foundational questions at the interface of quantum mechanics and gravity using magnetically and optically controlled diamond microcrystals. These micron-scale particles, containing nitrogen-vacancy (NV) centers, are levitated in a hybrid magneto-gravitational trap that enables exceptional isolation from the environment and long-lived mechanical coherence. By coherently coupling the NV center spin to the center-of-mass motion via magnetic field gradients, we aim to prepare non-classical superposition states of the particle’s position and probe their decoherence over time. The built-in spin sensor provides a uniquely quantum handle for preparation and readout of motion, while the mechanical oscillation frequency of the levitated particle is explicitly gravity-dependent, opening pathways for quantum-enhanced gravimetry. I will present recent advances in trap design, quantum-limited optical measurements, spin control, and motional state preparation. This approach provides a route to measure position-space decoherence and could enable future tests of gravitational effects on quantum systems at mesoscopic scales.
 

Ron Folman
Ben-Gurion University of the Negev

Experiments at the interface of general relativity and quantum mechanics
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The two pillars of modern physics are the theories of general relativity and quantum mechanics. After decades of theoretical attempts to unify these two pillars under one theoretical framework (often referred to as quantum-gravity), these pillars remain independent. To some, this situation is so unnatural that they claim it actually hints that at least one of the theories is wrong in some fundamental way. As technology in quantum-optics labs improves, new experiments — working at the interface of these two theories — can be realized. Such experiments will hopefully provide new insights that will eventually allow for the sought-after unification to be finally achieved.

In this talk, I will present three experiments conducted at this interface, two already realized and one planned. The first involves clock interferometry, in which a single clock in a spatial superposition experiences two different proper times due to gravitationally induced red shift. The second involves the observation of the Einsteinian equivalence principle, measured in the quantum domain. While the first two were realized with atoms, the third involves massive objects, specifically, nano-diamonds. Leaping by ten orders of magnitude in mass relative to the atomic experiments, the third experiment makes use of so-called active mass, where not only, but also, the gravitational field of earth needs to be taken into account.
 

Giorgio Gratta
Stanford University

A new look at Mossbauer spectroscopy for fundamental physics and nuclear quantum optics
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I will be describing the progress of a novel technique to search for new interactions at the sub-micrometer scale using Mossbauer spectroscopy. Indeed, nuclei are isolated affairs! Used as sensors, they are substantially less liable to external electromagnetic perturbations, making them well suited for searches at distances where atomic matter is affected by overwhelming backgrounds. The sensing is achieved by exploiting the exceedingly narrow resonances of Mossbauer spectroscopy.

In fact, the intrinsic insensitivity of nuclei to electromagnetic effect is also the reason why nuclear clocks may one day offer advantages over the atomic ones. Expanding the horizon in this area, I will also describe some advances in the exotic world of nuclear quantum optics.
 

Jason Hogan
Stanford University
Testing atom charge neutrality with atom interferometry

The apparent equality of the electron and proton charges is of great significance to fundamental physics, yet it remains an empirical question. The current experimental limit on the fractional electron-proton charge difference is below 10-21, set using classical physics techniques. We are developing a new quantum test based on the scalar Aharonov-Bohm effect in an atom interferometer, with the potential to improve this sensitivity by several orders of magnitude. I will give an update on the state of construction of the atom interferometer drop tower and the in-vacuum electrodes used to apply a potential difference across the atom’s wavefunction. I will also discuss recent progress in understanding the role of image charges from nearby conductors, which can potentially screen the signal, and describe how this effect can be mitigated through an appropriate electrode charging scheme.
 

Alan Jamison
University of Waterloo

CP Violation in Ultracold FrAg
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Violation of the CP symmetry at levels beyond those found in the Standard Model is a key component to answering the fundamental question of why we have matter in the universe. The REDRUM collaboration reports our progress toward a next-generation measurement searching for CP violation in ultracold radioactive FrAg molecules. We have produced new results in the cooling of Ag and Fr atoms separately, while making progress on a new source for the radioactive element Fr that will allow us to produce FrAg molecules year-round in a purely table-top experiment. We also report theoretical work in molecular structure that charts a path for producing ultracold FrAg molecules as well as understanding potential systematic effects in our future search for CP violation.
 

Shimon Kolkowitz
University of California, Berkeley

Precision timekeeping meets fundamental physics
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Optical atomic clocks not only deliver exceptional precision in timekeeping but also provide a powerful platform for testing fundamental physics. In this talk, we will present progress towards bridging quantum mechanics and gravity with tabletop optical clock experiments. We will present on three new experimental platforms, two at JILA and one at UC Berkeley, including a Wannier–Stark strontium optical lattice clock that has achieved record-breaking stability and accuracy, enabling gravitational redshift measurements at the sub-millimeter scale, an entangled optical clock that leverages quantum spin squeezing to generate many-body entanglement and thereby surpass the standard quantum limit, and a multi-ensemble optical lattice clock capable of applying large accelerations to the strontium atoms. We will show how such platforms enable the exploration of the interplay of quantum mechanics, gravitational effects, and photon-mediated interactions through first signatures of nonclassical proper time evolution, as well as through entanglement generation and frequency synchronization.
 

Gavin Morley
University of Warwick

Levitating nanodiamonds towards a test of the quantum nature of gravity
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We levitate nanodiamonds in vacuum, towards tests of fundamental physics. We have made nanodiamonds containing single nitrogen-vacancy (NV) centres with the longest spin coherence times. We aim to use a spin superposition of an NV centre to put the diamond into a superposition of being in two places at once, using an inhomogeneous magnetic field. This is the first step of a more ambitious experiment to test if gravitational effects can be in a quantum superposition: if gravitational effects can be in a quantum superposition, then gravity could entangle two such diamonds. We have a project called “Macroscopic superpositions towards witnessing the quantum nature of gravity (MAST-QG)”.
 

Lyman Page
Princeton University

PXS: A new search for ueV-scale axions
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Axions are an exciting dark matter candidate that can also resolve the strong CP problem. We describe a new axion search experiment, PXS, that operates in the 200–500 MHz band (0.8–2 ueV), the transitional mass range between the Axion Dark Matter eXperiment, which has set limits at the Dine–Fischler–Srednicki–Zhitnitsky sensitivity, and the Dark Matter Radio program. The experiment benefits from recent advances on a number of fronts. PXS’s three core elements are (1) a new 5 Tesla conduction-cooled NbTi magnet being developed by Yuhu Zhai’s group at PPPL, (2) a <50 mK resonator and readout being developed at Princeton, and (3) quantum-noise limited amplifiers being developed by Peter Day’s group at Jet Propulsion Laboratory. We briefly describe progress on each and how we plan for them to come together.
 

Ben Safdi
University of California at Berkeley

Why Axions Could Be the Next Big Discovery in Physics
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Axions have emerged as one of the most compelling candidates for new physics beyond the Standard Model. They provide an elegant solution to the strong CP problem of quantum chromodynamics, they naturally arise in many extensions of the Standard Model, including string theory, and they may constitute the dark matter that pervades our universe. I will review these motivations and explain why a broad range of current and planned experiments may be poised to detect axions for the first time, opening a new window onto fundamental physics and cosmology.
 

Michael Tarbutt
Imperial College London
Measuring the electron’s electric dipole moment with ultracold YbF molecules
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I will describe two experiments to measure the electron’s electric dipole moment (eEDM) using laser-cooled YbF molecules. The first uses a highly collimated beam of molecules cooled below 100 𝜇K in the two transverse directions. We measure their spin precession as they fly through a region of the large electric field. I will present recent data characterizing the sensitivity of this experiment and our efforts to control the dominant sources of noise and systematic error. The second experiment, still under development, will use molecules trapped in an optical lattice. We decelerate the molecules to low velocity using radiation pressure and deliver them to a magneto-optical trap. I will present our progress on slowing and trapping and our design of the eEDM apparatus.
 

Karl van Bibber
University of California at Berkeley

ALPHA — a plasma haloscope for the post-inflation axion
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Two of the most long-standing puzzles in physical science today bridging the smallest and largest distance scales in the cosmos are the strong-CP problem, i.e., the absence of a neutron electric dipole moment, and the nature of the dark matter of the universe. Standing at their intersection, and possibly the answer to both, is an ultralight elementary particle with extraordinarily weak couplings to ordinary matter and radiation — the axion. Arising out of theoretical work almost half a century ago, this light cousin of the neutral pion has remained elusive in the laboratory, and ironically our best prospects for its discovery will be to discover it as the ubiquitous dark matter. The most sensitive axion searches today rely on listening for a very weak radio signal from a microwave cavity immersed in a strong magnetic field. Owing to the expected signal strength, a trillionth of a trillionth of a watt, these axion haloscopes have been a major driver of quantum sensing technology, the most sensitive of them involving squeezed vacuum states to circumvent fundamental limits on quantum noise.

Problematically, the most recent predictions for the mass (= frequency) of axions created after inflation now lie above where conventional microwave cavities could produce useful conversion power; they simply become too small. An inspired solution to this conundrum was proposed, however, by which a microwave cavity would be replaced by a metamaterial, effectively an artificial plasma whose frequency could be designed to be arbitrarily high without loss of volume. A dedicated international team explored the practicality of this scheme over several years and developed a conceptual design for an experiment, which is now under construction at Yale University under an award from the “Small Experiments” solicitation.

This talk with present a brief background to the axion in particle physics and cosmology, the beautiful phenomena of wire-medium metamaterials, the Axion Longitudinal Plasma HAloscope (ALPHA) project and its search potential. Finally will be a brief glimpse into the new field of axioastronomy that will be opened up after its discovery.

This work was supported by the Simons Foundation under grant MP-TMPS-00003000, and the John F. Templeton Foundation under grant 63120.
 

Amar Vutha
University of Toronto

T-violation searches with octupolar nuclei in crystals

Our approach to precision measurements uses polarized atomic ions containing octupolar nuclei in crystals. This platform has attractive properties for improving the reach of searches for time-reversal symmetry (T) violation, both static (due to T-odd new physics) and oscillatory (due to wavy dark matter). We have built an apparatus and conducted a first round of measurements to explore this approach.

I will report on our findings from the last year, which have led us to an improved understanding of the challenges and opportunities for precision measurements with ions in crystals.