Quantum superposition at the half-metre scale

Abstract

The quantum superposition principle allows massive particles to be delocalized over distant positions. Though quantum mechanics has proved adept at describing the microscopic world, quantum superposition runs counter to intuitive conceptions of reality and locality when extended to the macroscopic scale, as exemplified by the thought experiment of Schrödinger's cat. Matter-wave interferometers, which split and recombine wave packets in order to observe interference, provide a way to probe the superposition principle on macroscopic scales and explore the transition to classical physics. In such experiments, large wave-packet separation is impeded by the need for long interaction times and large momentum beam splitters, which cause susceptibility to dephasing and decoherence. Here we use light-pulse atom interferometry to realize quantum interference with wave packets separated by up to 54 centimetres on a timescale of 1 second. These results push quantum superposition into a new macroscopic regime, demonstrating that quantum superposition remains possible at the distances and timescales of everyday life. The sub-nanokelvin temperatures of the atoms and a compensation of transverse optical forces enable a large separation while maintaining an interference contrast of 28 per cent. In addition to testing the superposition principle in a new regime, large quantum superposition states are vital to exploring gravity with atom interferometers in greater detail. We anticipate that these states could be used to increase sensitivity in tests of the equivalence principle, measure the gravitational Aharonov-Bohm effect, and eventually detect gravitational waves and phase shifts associated with general relativity.

Inertial quantum sensors using light and matter

“…Nevertheless, our quest for improving the sensitivity of ground-based atom interferometers will soon reach a limit imposed by gravity and by the requirements of ultra-high vacuum and a very well controlled environment. Current state-of-the-art experimental apparatuses allow for seconds of interrogation with 10 to 120 meters of free-fall [69,70,71,72,67]. Space-based applications ‡, currently under study, will enable physicists to increase even further the interrogation time, thereby increasing dramatically the sensitivity and accuracy of atom interferometers.…”

“…to observe a strong signal), while combining temperature of atom clouds very close to the absolute zero (1 microKelvin) and thus to reach regimes where the wave behavior of the atoms becomes significant. Nevertheless, the quest to reach higher sensitivity requires (i) reducing the velocity dispersion of the atomic sample [66] in order to allow for enhanced enclosed area via larger momentum splitting [67], (ii) increasing the interrogation time, or (iii) increasing the knowledge of the scaling factor, which depends directly on the initial velocity of the atoms and can be better controlled with more confined atomic sources.…”

Ultracold metastable helium: Ramsey fringes and atom interferometry

“…This allows easy wavepacket separation over macroscopic distances with only a few photon recoils. To illustrate this we compare the recent large 0.54 m wavepacket splitting obtained with Rb in the 10 m fountain in Stanford [34]. This was realized after 1.04 s ballistic flight following 45 consecutive Bragg pulses providing 90 k wavepacket splitting.…”

Two-dimensional grating magneto-optical trap

“…Matter wave interferometry has demonstrated orders of magnitude improvement over a wide range of precision measurements [1][2][3][4][5][6][7][8]. These successes have spurred interest in transitioning cold atom devices from the lab to more demanding environments [9][10][11][12][13][14][15][16][17].…”