Atom Interferometry. Prof. Mark Kasevich Dept. of Physics and Applied Physics Stanford University, Stanford CA. Young’s double slit with atoms. Young’s 2 slit with Helium atoms. Interference fringes.
Prof. Mark Kasevich
Dept. of Physics and Applied Physics
Stanford University, Stanford CA
Young’s 2 slit with Helium atoms
One of the first experiments to demonstrate de Broglie wave interference with atoms, 1991 (Mlynek, PRL, 1991)
As atom climbs gravitational potential, velocity decreases and wavelength increases
Sagnac effect for de Broglie waves
(longer de Broglie wavelength)
Current ground based experiments with atomic Cs: Wavepacket spatial separation ~ 1 cm
Phase shift resolution ~ 10–5 rad
(Previous experiments with neutrons)
Resonant optical interaction
Resonant traveling wave optical excitation, (wavelength l)
Laser cooling techniques are used to achieve the required velocity (wavelength) control for the atom source.
Laser cooling: Laser light is used to cool atomic vapors to temperatures of ~10-6 deg K.
Three contributions to interferometer phase shift:
Laser fields (Raman interaction):
Wavepacket separation at detection:
See Bongs, et al., quant-ph/0204102 (April 2002) also App. Phys. B, 2006.
Measured gyroscope output vs.orientation:
Typical interference fringe record:
Pb mass translated vertically along gradient measurement axis.
Yale, 2002 (Fixler PhD thesis)
Characterization of source mass geometry and atom trajectories (with respect to source mass) allows for determination of Newton’s constant G.
Use gravity gradiometer to reject spurious technical vibrations.
Systematic error sources dominated by initial position/velocity of atomic clouds.
dG/G ~ 0.3%
Fixler, et al., Science, 2007, also Fixler PhD thesis, 2003.
~ 1 m
Applications in precision navigation and geodesy
Demonstrated accelerometer resolution: ~10-11 g.
ESIII loading platform survey site
Gravity anomally map from ESIII facility
Gravity gradient survey of ESIII facility
Using new sensors, we anticipate dG/G ~ 10-5.
This will also test for deviations from the inverse square law at distances from l ~ 1 mm to 10 cm.
Theory in collaboration with S. Dimopoulos, P. Graham, J. Wacker.
Co-falling 85Rb and 87Rb ensembles
Evaporatively cool to < 1 mK to enforce tight control over kinematic degrees of freedom
dg ~ 10-15 g with 1 month data collection
dg ~ 10-16 limited by magnetic field inhomogeneities and gravity anomalies.
Also, new tests of General Relativity
10 m atom drop tower
10 m drop tower
Atom and photon geodesics
Collaborators: Savas Dimopoulos, Peter Graham, Jason Hogan.
Prior work, de Broglie interferometry: Post-Newtonian effects of gravity on quantum interferometry, Shigeru Wajima, Masumi Kasai, Toshifumi Futamase, Phys. Rev. D, 55, 1997; Bordé, et al.
Schwazchild metric, PPN expansion:
Corresponding AI phase shifts:
Projected experimental limits:
(Dimopoulos, et al., PRL 2007)
Distance between objects modulates by hL, where h is strain of wave and L is their average separation.
Interesting astrophysical objects (black hole binaries, white dwarf binaries) are sources of gravitational radiation in 0.01 – 10 Hz frequency band.
LIGO is existing sensor utilizing long baseline optical interferometry. Sensitive to sources at > 40 Hz.
Differential accelerometer configuration for gravity wave detection.
Atoms provide inertially decoupled references (analogous to mirrors in LIGO)
Gravity wave phase shift through propagation of optical fields.
Previous work: B. Lamine, et al., Eur. Phys. J. D 20, (2002); R. Chiao, et al., J. Mod. Opt. 51, (2004); S. Foffa, et al., Phys. Rev. D 73, (2006); A. Roura, et al., Phys. Rev. D 73, (2006); P. Delva, Phys. Lett. A 357 (2006); G. Tino, et al., Class. Quant. Grav. 24 (2007).
Satellite configuration (dashed line indicates atom trajectories)
Lasers, optics and photodetectors located in satellites S1 and S2.
Atoms launched from satellites and interrogated by lasers away from S1 and S2.
Configuration is free from many systematic error sources which affect proposed sensors based on macroscopic proof masses.
DUSEL facility: 1 km vertical shaft at Homestake mine. In the future, deeper shafts may be available.
Seismic noise induced strain analysis for LIGO (Thorne and Hughes, PRD 58)
Seismic fluctuations give rise to Newtonian gravity gradients which can not be shielded.
Primary disturbances are surface waves. Suggests location in underground facility.
Sub-surface installation may be sufficiently immune to seismic noise to allow interesting ground-based sensitivity limits.
Collaboration with SDSU, UofTenn, NASA Ames to install protoptype sensor.
Also, next generation seismic sensors (John Evans, USGS).
(data courtesy of Vuk Mandic, UofM)
Are there (local) observable phase shifts of cosmological origin?
Analysis has been limited to simple metrics:
No detectable local signatures for Hubble expansion (shift ~H2)
Interesting phenomenology from exotic/speculative theories?
How do we exploit this sensitivity?
Df ~ mgzT/h
Gravitational phase shift scales linearly with mass of interfering particle (quasi-particle).
Therefore, improved sensitivity with increased mass for interfering particle.
Molecules, C60, etc.
QND correlated many-body states Weakly bound quasi-particles
Possible interference with >106 amu objects. Entanglement via gravitational interaction?
Are there fundamental limits?
Non-linearity in quantum mechanics
Space-time fluctuations (eg. due to Planck–scale fluctuations)
In coming years, AI methods will provide a >106-fold improvement in sensitivity to such physics.