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We report the experimental observation of rectified momentum transport for a Bose-Einstein Condensate kicked at the Talbot time (quantum resonance) by an optical standing wave. Atoms are initially prepared in a superposition of the 0 and −2 k l momentum states using an optical π/2 pulse. By changing the relative phase of the superposed states, a momentum current in either direction along the standing wave may be produced. We offer an interpretation based on matter wave interference, showing that the observed effect is uniquely quantum.The current interest in rectified atomic diffusion, or atomic ratchets, may be traced back to fundamental thermodynamical concerns [1] and also the desire to understand the so-called "Brownian motors" linked to directed diffusion on a molecular scale [2,3]. Abstractly, the ratchet effect may be defined as the inducement of directed diffusion in a system subject to unbiased perturbations due to a broken spatio-temporal symmetry.Given the scale on which such microscopic ratchets must work, it is not surprising that the concept of quantum ratchets has recently augmented this area of investigation. The addition of quantum effects such as tunneling gives rise to new ratchet phenomena such as current reversal [4]. Whilst early quantum ratchet investigations, both theoretical and experimental, have focussed on the role of dissipative fluctuations in driving a ratchet current [5], recent theory has considered the possibility of Hamiltonian ratchets, where the diffusion arises from Hamiltonian chaos rather than stochastic fluctuations [6]. This has lead to proposals [7,8] and even an experimental realisation [9] for ratchet systems realised using atom optics, in the context of the atom optics kicked rotor [10] where periodic pulses from an optical standing wave kick atoms into different momentum states.It is generally accepted that a ratchet effect cannot be produced without breaking the spatio-temporal symmetry of the kicked rotor system. In Ref.[9], a rocking sine wave potential was combined with broken time symmetry of the kicking pulses to effectively realise such a system in an experiment. Other schemes involve the use of quantum resonance (QR) to drive the ratchet effect. At QR, atoms typically exhibit linear momentum growth symmetrical about the initial mean momentum. However it has been suggested that merely breaking the spatial symmetry of the kicked rotor at QR may be sufficient to produce a ratchet current [11]. In this letter we present the first experimental evidence of such a resonant ratchet effect in which the underlying mechanism is purely quantum. Our system uses a Bose-Einstein condensate (BEC) kicked by an optical standing wave [12], but there is no asymmetry in either the kicking potential * Electronic address: mark@ils.uec.ac.jp or the period of the kicks, (which is set to the Talbot time T T corresponding to quantum resonance [13]). Rather, the observed directed diffusion is a property of the initial atomic wavefunction (which we prepare before kicking) in the presenc...

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We demonstrate a precision frequency measurement using a phase-stabilized 120-km

We report on the first joint search for gravitational waves by the TAMA and LIGO collaborations. We looked for millisecond-duration unmodeled gravitational-wave bursts in 473 hr of coincident data collected during early 2003. No candidate signals were found. We set an upper limit of 0.12 events per day on the rate of detectable gravitational-wave bursts, at 90% confidence level. (2005) 122004-3 simulations, we estimate that our detector network was sensitive to bursts with root-sum-square strain amplitude above approximately 1-3 10 ÿ19 Hz ÿ1=2 in the frequency band 700-2000 Hz. We describe the details of this collaborative search, with particular emphasis on its advantages and disadvantages compared to searches by LIGO and TAMA separately using the same data. Benefits include a lower background and longer observation time, at some cost in sensitivity and bandwidth. We also demonstrate techniques for performing coincidence searches with a heterogeneous network of detectors with different noise spectra and orientations. These techniques include using coordinated software signal injections to estimate the network sensitivity, and tuning the analysis to maximize the sensitivity and the livetime, subject to constraints on the background.

Optical frequency at 1542 nm was coherently transferred over a 120-km-long installed telecom fiber network between two cities (Tsukuba and Tokyo) in Japan separated by more than 50 km. The phase noise induced by the fiber length fluctuations was actively reduced by using a fiber stretcher and an acousto-optic modulator. The fractional frequency instability of the one-way transmitted light was reduced down to less than 8.0 x 10(-16) at an averaging time of 1s, which is limited by the theoretical limit deduced from the length and the intrinsic noise of the fiber.

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A Mach-Zehnder-type atom interferometer with a Bose-Einstein condensate has been investigated on an atom chip by using optical Bragg diffraction. A phase shift and a contrast degradation, which depend on the atomic density and the trapping frequency of the magnetic-guide potential, have been observed. Also, the output wave packets were found to exhibit a spatial interference pattern. The atom-atom interaction and the guide potential induce the spatially inhomogeneous phase evolution of the wave packets in each arm of the interferometer. The observed contrast degradation can be quantitatively explained as a dephasing due to this inhomogeneous phase evolution.