A gentle reminder…

Please join us for a seminar sponsored by the Atomic and Molecular Physics Division, Harvard-Smithsonian Center for Astrophysics. Complete schedule at http://www.cfa.harvard.edu/amp/events.html

11:00 AM Monday, February  4, 2013
Phillips Auditorium
60 Garden St, Cambridge, MA

Title: Matter-wave clocks
Author: Holger Müller

Matter-wave clocks 

Holger Müller, UC Berkeley

It is a key principle of quantum mechanics that plane matter waves are proportional to exp(-ip_μx^μ/ℏ)=exp(-iω₀τ), where p_μ and x^μ are respectively 4-momentum and position, and τ is the proper time measured along the particle’s trajectory. Thus, the quantum state of a free particle of mass m accumulates the same phase as a clock ticking at the particle’s Compton frequency of ω₀=mc²/ℏ travelling along the particle’s trajectory. This implies that a single particle can be a reference for a clock. In principle, such a clock could be built by annihilating particle-antiparticle pairs and counting the frequencies of the generated photons. This would provide a frequency reference with virtually infinite quality factor Q and unsurpassed stability against systematic influences. The frequency (ω₀/2π=3×10²⁵ Hz for a Cesium atom), however, is far beyond modern counting techniques. A method to divide it into a technically accessible range is thus required.

We demonstrate a “Compton clock,” a clock referenced to ω₀, using an optical frequency comb to self-reference a Ramsey-Bordé atom interferometer and synchronize an oscillator at a subharmonic of ω₀ . The interferometer is based on n-photon Bragg diffraction. It is self-referenced by locking the laser to the N^th multiple of the measured recoil frequency. The clock’s frequency ω_m=ω₀/(2nN²)  is then fully determined by ω₀ and the known numerical factors N² and n. The clock has an accuracy and stability of 4×10^-9. It highlights the intimate connection between frequency and mass: The Compton frequency can serve as a frequency reference directly, without requiring the particle to be annihilated. It allows measurement of microscopic masses with 4×10^-9 accuracy in the proposed revision to SI units. Together with the Avogadro project, it yields calibrated kilograms. We will survey other applications of matter waves as clocks, such as testing relativity and verifying the gravitational Aharonov-Bohm effect.

Reference:

A clock directly linking time to a particle’s mass. Shau-Yu Lan, Pei-Chen Kuan, Brian Estey, Damon English, Justin Brown, Michael Hohensee, and Holger Müller, Science, http://dx.doi.org/10.1126/science.1230767 (2013).

Regards,
Gang

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Gang Li

Post-doctoral fellow

Atomic and Molecular Physics Division

Harvard-Smithsonian Center for Astrophysics

Cambridge

USA

Tel: 6174962593