Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Optical rogue waves wikipedia , lookup
Thomas Young (scientist) wikipedia , lookup
Optical coherence tomography wikipedia , lookup
Photonic laser thruster wikipedia , lookup
Rutherford backscattering spectrometry wikipedia , lookup
Harold Hopkins (physicist) wikipedia , lookup
Ultrafast laser spectroscopy wikipedia , lookup
Nonlinear optics wikipedia , lookup
Precision Atom Interferometry Prof. Mark Kasevich Dept. of Physics and Applied Physics Stanford University, Stanford CA Outline Light-pulse de Broglie wave interferometry overview Existing Sensors Rotation (Gyroscope) Gravimetric (Gravity Gradiometer) Sensors for Science Testing Newton’s inverse square law Equivalence principle Gravity beyond Newton Gravity wave detection Testing atomic charge neutrality Quantum Metrology Young’s double slit with atoms Young’s 2 slit with Helium atoms Interference fringes Slits One of the first experiments to demonstrate de Broglie wave interference with atoms, 1991 (Mlynek, PRL, 1991) (Light-pulse) atom interferometry Resonant optical interaction |2〉 |1〉 2-level atom Resonant traveling wave optical excitation, (wavelength λ) Recoil diagram Momentum conservation between atom and laser light field (recoil effects) leads to spatial separation of atomic wavepackets. Phase shift calculation methodology Three contributions to interferometer phase shift: Propagation shift: Laser fields (Raman interaction): Wavepacket separation at detection: See Bongs, et al., quant-ph/0204102 (April 2002) also App. Phys. B, 2006. Laser cooling 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. Image source:www.nobel.se/physics Laboratory gyroscope Gyroscope interference fringes: AI gyroscope Sensor noise Noise: 3 µdeg/hr1/2 Bias stability: < 60 µdeg/hr Scale factor: < 5 ppm Atom shot noise Gustavson, et al., PRL, 1997, Durfee, et al., PRL, 2006 Lab technical noise Measurement of Newton’s Constant Use differential atom interferometer accelerometers (rejects spurious technical vibrations). Pb mass translated vertically along gradient measurement axis. Yale, 2002 (Fixler PhD thesis) Characterization of source mass geometry and atom trajectories allows for determination of Newton’s constant G. Measurement of G Systematic error sources dominated by initial position/velocity of atomic clouds. δG/G ~ 0.3% Fixler PhD thesis, 2003; Fixler, et al., Science, 2007. Differential accelerometer ~1m Applications in precision navigation and geodesy Gravity gradiometer Demonstrated accelerometer resolution: ~1x10-11 g. Gravity gradient survey Gravity anomally map from ESIII facility (top view) Gravity gradient survey of ESIII facility Test Newton’s Inverse Square Law Using new sensors, we anticipate δG/G ~ 10-5. This will also test for deviations from the inverse square law at distances from λ ~ 1 mm to 10 cm. Theory in collaboration with S. Dimopoulos, P. Graham, J. Wacker. Compact gyroscope Measured gyroscope output vs.orientation: Typical interference fringe record: • Inferred ARW: < 100 µdeg/hr1/2 • 10 deg/s max input • <100 ppm absolute accuracy A quantum sensor …. coherence length Measurement of coherence length of laser cooled atomic source (~ 100 nm) Time-skewed pulse sequence to reject spurious mutli-path interferences Interior view of sensor UHV vacuum enclosure; Cs atomic source Discrete optics for laser beams, magnetic field control; photodiodes …. Equivalence Principle Use atom interferometric differential accelerometer to test EP Co-falling 85Rb and 87Rb ensembles Evaporatively cool to < 1 µK to enforce tight control over kinematic degrees of freedom Statistical sensitivity δg ~ 10-15 g with 1 month data collection Systematic uncertainty δg ~ 10-16 g limited by magnetic field inhomogeneities and gravity anomalies. Atomic source 10 m drop tower Post-Newtonian gravitation Light-pulse interferometer phase shifts for Schwarzchild metric: • Geodesic propagation for atoms and light. • Path integral formulation to obtain quantum phases. laser atom Post-Newtonian trajectories for classical particle: • Atom-field interaction at intersection of laser and atom geodesics. 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. Parameterized Post-Newtonian (PPN) analysis Schwazchild metric, PPN expansion: Steady path of apparatus improvements include: Corresponding AI phase shifts: • Improved atom optics • Taller apparatus • Sub-shot noise interference readout Projected experimental limits: • In-line, accelerometer, configuration (milliarcsec link to external frame not req’d). (Dimopoulos, et al., PRL 2007, PRD 2008) Error Model Use standard methods to analyze spurious phase shifts from uncontrolled: • Rotations • Gravity anomalies/gradients • Magnetic fields • Proof-mass overlap • Misalignments • Finite pulse effects Known systematic effects appear controllable at the δg ~ 10-16 g level. Gravity Wave Detection 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. Gravity Wave Detection Metric: 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. Gravity wave induced phase shift: h is strain, L is separation, T is pulse separation time, ω is frequency of wave 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). Proposed Terrestrial Detector Performance 1 km Dimopoulos, Graham, Hogan, Kasevich, Rajendran, 2008 (archive, submitted) Seismic Noise Seismic noise induced strain analysis for LIGO (Thorne and Hughes, PRD 58) . Primary disturbances are surface waves. Suggests location in underground facility. Seismic fluctuations give rise to Newtonian gravity gradients which can not be shielded. Data courtesy of Vuc Mandic Satellite Configuration Lasers, optics and photodetectors located in satellites S1 and S2. Atoms launched from satellites and interrogated by lasers away from S1 and S2. Atomic Physics Technical Challenges • Advanced, high flux atom source development – high rep rate, high flux source of cold atoms – 10 Hz, 108 atoms/shot – requires incremental advances in current technology • Large momentum transfer atom optics – – – – Enhances sensitivity Demonstrated N ~ 10 Desired N ~ 100 Work in progress Atom charge neutrality • Apparatus will support >1 m wavepacket separation • Enables ultra-sensitive search for atom charge neutrality through scalar Aharonov-Bohm effect. ε = δe/e ~ 10-26 for mature experiment using scalar Aharonov-Bohm effect Current limit: δe/e ~ 10-20 (Unnikrishnan et al., Metrologia 41, 2004) Impact of a possible observed imbalance currently under investigation. Phase shift: Theory collaborators: A. Arvanitaki, S. Dimopoulos, A. Geraci, PRL 2008. Quantum Metrology: Sub-shot noise detection Atom shot noise limits sensor performance. Recently evolving ideas in quantum information science have provided a road-map to exploit exotic quantum states to significantly enhance sensor performance. – Sensor noise scales as 1/N where N is the number of particles – “Heisenberg” limit – Shot-noise ~ 1/N1/2 limits existing sensors Challenges: – Demonstrate basic methods in laboratory – Begin to address engineering tasks for realistic sensors Impact of successful implementation for practical position/time sensors could be substantial. Possible 10x – 100x reduction in sensor noise. Enables crucial trades for sensitivity, size and bandwidth. QND atom detection in high finesse cavity Dispersive cavity shift MOT located in 300 µm waist of 200K finesse (3 kHz linewidth) optical cavity. Cavity frequency shift (kHz) 7 6 5 4 3 2 1 0 100 200 300 400 500 Microwave pulse duration (microseconds) (Poster, Igor Teper; Tuchman, et al. PRA, 2006, Long, Opt. Lett., 2007) Rabi oscillations detected via cavity shift State evaluation via QND back-action Use QND probe to prepare spin squeezed state. Measurement backaction: dispersion in AC Stark shift due to photon number fluctuations associated with coherent optical state in cavity. Observe back-action by rotation of atomic state on Bloch sphere using a microwave pulse. Measured number fluctuations (induced by QND back-action) agree with theory. Control 2.5 nW probe 1.2 nW probe Acknowledgements – – – – – – – – – – – – – – Grant Biedermann, PhD, Physics Ken Takase, PhD, Physics Igor Teper, Post-doctoral fellow John Stockton, Post-doctoral fellow Louis Delsauliers, Post-doctoral fellow Xinan Wu, Graduate student, Applied physics Jongmin Lee, Graduate student, Electrical engineering Chetan Mahadeswaraswamy, Graduate student, Mechanical engineering David Johnson, Graduate student, Aero/Astro engineering Geert Vrijsen, Graduate student, Applied physics Jason Hogan, Graduate student, Physics Sean Roy, Graduate student, Physics Tim Kovachy, Undergraduate Paul Bayer, Engineer + THEORY COLLABORATORS: S. Dimopolous, P. Graham, S. Rajendran, A. Arvanitaki, A. Geraci + AOSense team B. Young, T. Gustavson, J. Spilker, A. Black, F. Roller, T. Tran, M. Mathews, A. Vitushkin, B. Dubetsky.