Paired-atom laser beams created via four-wave mixing

Abstract

A method to create paired atom laser beams from a metastable helium atom laser via fourwave mixing is demonstrated. Radio frequency outcoupling is used to extract atoms from a Bose Einstein condensate near the center of the condensate and initiate scattering between trapped and untrapped atoms. The unequal strengths of the interactions for different internal states allows an energy-momentum resonance which leads to the creation of pairs of atoms scattered from the zerovelocity condensate. The resulting scattered beams are well separated from the main atom laser in the 2-dimensional transverse atom laser profile. Numerical simulations of the system are in good agreement with the observed atom laser spatial profiles, and indicate that the scattered beams are generated by a four-wave mixing process, suggesting that the beams are correlated.PACS numbers: 03.75. Pp,03.75.Nt,67.85.Jk Sources of matter waves gained a dramatic improvement with the achievement of Bose-Einstein condensation (BEC) in dilute gases and the development of the atom laser [1,2]. Like optical lasers before them, atom lasers can produce Heisenberg-limited beam profiles [3,4] and promise high spectral density through their dramatically lower linewidth [5]. Another exciting possibility resulting from having such a coherent source of atoms is the generation of non-classical matter waves through entangled beams. Such entangled beams are useful for tests of quantum mechanics, and are required to perform Heisenberg-limited interferometry [6,7]. In this Letter, we show that the asymmetric scattering rates between internal states of metastable helium (He*) cause welldefined peaks in the output of an atom laser. These peaks are due to a four-wave mixing (FWM) process, and are experimentally demonstrated.A nonlinear process is required to produce entanglement, and one of the advantages of atomic systems over optical systems is that there are strong inherent nonlinearities due to the atomic interactions, although these interactions can also lead to complications. These nonlinearities allow certain analogs of nonlinear optical experiments such as FWM and Kerr squeezing to be performed directly in the atomic sample [8]. Both of these produce entanglement in optical systems. FWM in a trapped BEC has been demonstrated experimentally in configurations where three distinct momentum states generated a fourth [9], and where two momentum states generated a pair of correlated atomic beams [10]. These experiments demonstrated that the output was phase coherent, but the correlation properties were not measured. More recently the pair correlations in a spontaneous scattering of two colliding condensates were measured using the single atom detectors available for He* atoms [11].Using these existing sources of entangled pairs of atoms for interferometric experiments will be complicated by the high densities of the sources, where the nonlinearities that generated the correlations ultimately degrade the long term coherence of the sample. While recent experiments have inc...

Cold and trapped metastable noble gases

“…¿From a fundamental perspective, atom lasers can be used to study atom-atom interactions (Döring et al, 2008) as well as coherent properties (Bloch et al, 2000) of matter waves. Atomic scattering is responsible for non-linearities in atom laser formation, which can gener-ate non-classical matter waves such as entangled beams (Dall et al, 2009). Such beams are of interest for tests of quantum mechanics (Reid et al, 2009), and for performing Heisenberg-limited interferometry (Dowling, 1998).…”

“…Thus MCP's have been widely used in the cold metastable atom community as an alternative or a complement to optical imaging. Imaging is possible by placing a phosphor screen behind the MCP and recording the phosphorescence with a camera (Dall et al, 2009;Lawall and Prentiss, 1994;Rauner et al, 1998;Shimizu et al, 1992). A drawback to the phosphor screen method is that it relies on a video camera to acquire the data, and thus the frame rate, or temporal resolution is necessarily limited by the video frame rate, typically 20 ms.…”

Anisotropy ins-wave Bose-Einstein condensate collisions and its relationship to superradiance

“…Finally, in a broader context, one expects other situations that generate a scattered atom halo, such as molecular dissociation in a condensate [36,37,[42][43][44][45][46][47][48], atomic parametric down-conversion [4,[49][50][51][52][53], or the interaction of a condensate with barriers and obstacles [54][55][56][57][58], to also be susceptible to the same anisotropy-producing processes. …”

Surpassing the standard quantum limit in an atom interferometer with four-mode entanglement produced from four-wave mixing

“…Atomic four-wave mixing [15] has long been considered a possible method of creating entanglement between spatially separated atomic modes [16][17][18][19][20][21][22][23], and the generation and detection of quantum correlations using this process has recently been demonstrated [24,25]. Four-wave mixing has an advantage over one-axis-twisting schemes because the correlations produced by the interaction are number correlations and are not as sensitive to the total number of particles.…”