Probing gravity by holding atoms for 20 seconds

Abstract

Atom interferometers are powerful tools for both measurements in fundamental physics and inertial sensing applications. Their performance, however, has been limited by the available interrogation time of freely falling atoms in a gravitational field. We realize an unprecedented interrogation time of 20 seconds by suspending the spatially-separated atomic wavepackets in a lattice formed by the mode of an optical cavity. Unlike traditional atom interferometers, this approach allows potentials to be measured by holding, rather than dropping, atoms. After seconds of hold time, gravitational potential energy differences from as little as microns of vertical separation generate megaradians of interferometer phase. This trapped geometry suppresses the phase sensitivity to vibrations by 3-4 orders of magnitude, overcoming the dominant noise source in atom-interferometric gravimeters. Finally, we study the wavefunction dynamics driven by gravitational potential gradients across neighboring lattice sites.Matter-wave interferometers with freely falling atoms have demonstrated the ability to precisely measure e.g., gravity [1] and fundamental constants [2,3], to test general relativity [4][5][6], and to search for new forces [7,8].A major obstacle to increasing their sensitivity, however, has been the limited time during which coherent, spatially-separated superpositions of atomic wave packets can be interrogated. Up to 2.3 seconds of interrogation time has been realized in a 10-meter atomic fountain [9], and several seconds of interrogation time are the target of experiments in fountains measuring hundreds of meters [10,11], zero-gravity planes [12], drop towers [13], sounding rockets [14], and the International Space Station [15][16][17]. Geometries that trap the interferometer in an optical lattice [18,19] have been explored, but attempts to date have suffered from dephasing in the trap.Here, we demonstrate 20 seconds of coherence in an atom interferometer held in an optical lattice, overcoming trap dephasing by using an optical cavity as a spatial mode-filter. After 20 seconds, sensitivity to vibrations is suppressed by 10 3 − 10 4 relative to traditional atomic gravimeters at the same sensitivity, due to the continuous accumulation of free evolution phase in the trapped wave packets. Trapping the interferometer allows for the sensitivity to be increased by extending interrogation times rather than wavepacket separations or free fall distances, reducing experimental complexity and potentially minimizing systematics.Our matter-wave interferometer builds upon the setup described previously in [7,20]. Cesium atoms are laser-cooled to ∼300 nK, prepared in the magneticallyinsensitive m F =0 state, and launched millimeters upwards into free fall (see Methods for details). In free fall, counter-propagating laser beams in the cavity manipulate the atomic trajectories. We stimulate two-photon Raman transitions between the hyperfine ground states of cesium, F = 3 and F = 4, imparting two photons' momenta to the atom with each lase...

Is Newtonian gravitational constant – a quantized constant of microscopic quantum gravity?

“…This relation seems to be satisfied at only one value of Error is around 865 ppm. It needs further study with respect to ongoing experiments [17][18][19][20]. Another interesting relation is, 21 10 30…”

Quantum-classical hypothesis tests in macroscopic matter-wave interferometry

“…A first beam splitter creates a superposition of two wave packets, occupied by a single atom or an entire BEC, which propagate on distinct paths, rejoin on a second beam splitter, and are then detected in the two associated output ports. Experimental demonstrations of such phasestable superposition states may be deemed macroscopic due to the large arm separations and long coherence times that can be achieved [10][11][12]33].…”

“…Even in this case, the interference pattern may fluctuate randomly from shot to shot due to technical noise in the beam splitters, timing uncertainties, or fluctuating background fields. In case of full dephasing, one expects the uniform phase average of the binomial count distribution (12) as given by…”

“…Attempts to explain the apparent absence of macroscopic superposition states, so-called Schrödinger cats, involve the many-world interpretation [2], decoherence theory [3][4][5], and gravitational [6,7] or spontaneous wave-function collapse [8,9]. At the same time, longstanding experimental efforts are pushing the frontiers of quantum mechanics to ever larger spatial [10,11], temporal [12], and mass [13,14] scales. Systematic methods to assess and compare the prospects of testing macrorealism with different experimental approaches could guide future developments and allocation of resources in the field.…”

Characterization of Errors in Interferometry with Entangled Atoms

“…Inertially sensitive AIs have many important practical applications [8,9,11], including accelerometers and gyroscopes [41][42][43][44][45], and gravimeters [46][47][48][49]. Promising advances also demonstrate gravity measurements using spatially separated atomic wave packets suspended in a lattice [50][51][52] and most recently with ultralong interrogation times [53].…”