Twin-atom beams

Abstract

We present highly efficient emission of twin-atom beams into a single transversal mode of a waveguide potential. The source is a one-dimensional degenerate Bose gas in the first radially excited state. We directly measure a suppression of fluctuations in the atom number difference between the beams to 0.37(3) with respect to the classical expectation, equivalent to 0.11(2) after correcting for detection noise. Our results underline the high potential of ultracold atomic gases as sources for quantum matter wave optics and will enable the implementation of schemes previously unattainable with massive particlesComment: 7 pages (including supplementary material), 5 figure

Noise-resistant optimal spin squeezing via quantum control

“…Since the early theoretical proposals to realize them with non linear interactions [2,3], spin squeezed states have been implemented in several experiments. Specific examples include generation of spin squeezed states in cavity QED [4][5][6], in trapped ions through shared motional modes [7,8] or using a Bose-Einstein condensate [9,10].In this Letter we demonstrate that optimal control can be effectively employed to produce highly squeezed spin states in many-body quantum systems, drastically reducing the impact of relaxation and decoherence. Other approaches applied control techniques creating spin squeezing as a succession of unitary pulses of a constant Hamiltonian [11][12][13].…”

Microscopic theory of a phase transition in a critical region: Bose–Einstein condensation in an interacting gas

“…It is immediate to generalize them to any trapping potentials and boundary conditions. They open a way to solve the long-standing problem of the BEC and other phase transitions [1][2][3][4][5][6][7][8][9][10][11][12], including a restricted canonical ensemble problem [2], and describe numerous modern laboratory and numerical experiments on the critical phenomena in BEC of the mesoscopic systems [22][23][24][25][26][27][28][29][30][31][32][33][34][35].…”

“…It becomes possible due to the newly developed methods of (a) the nonpolynomial averages and contraction superoperators [15,16], (b) the partial difference (recurrence) equations [17][18][19] (a discrete analog of the partial differential equations) for superoperators, and (c) a characteristic function and cumulant analysis for a joint distribution of the noncommutative observables. They allow us to take into account (I) the constraints in a many-body Hilbert space, which are the integrals of motion prescribed by a broken symmetry in virtue of a Noether's theorem, and constraintcutoff mechanism, responsible for the very existence of a phase transition and its nonanalytical features, [4,20,21] (II) an insufficiency of a grand-canonical-ensemble approximation, which is incorrect in the critical region [2,8] because of averaging over the systems with different numbers of particles, both below and above the critical point, i.e., over the condensed and noncondensed systems at the same time, that implies an error on the order of 100% for any critical function, (III) a necessity to solve the problem for a finite system with a mesoscopic (i.e., large, but finite) number of particles N in order to calculate correctly an anomalously large contribution of the lowest energy levels to the critical fluctuations and to avoid the infrared divergences of the standard thermodynamic-limit approach [5][6][7][8][9][10][11] as well as to resolve a fine structure of the λ-point, (IV) a fact that in the critical region the Dyson-type closed equations do not exist for true Green's functions, but do exist for the partial 1-and 2-contraction superoperators, which reproduce themselves under a contraction.The problem of the critical region and mesoscopic effects is directly related to numerous modern experiments and numerical studies on the BEC of a trapped gas (including BEC on a chip), where N ∼ 10 2 − 10 7 , (see, for example, [22][23][24][25][26][27][28][29][30][31][32][33]) and superfluidit...…”

“…The problem of the critical region and mesoscopic effects is directly related to numerous modern experiments and numerical studies on the BEC of a trapped gas (including BEC on a chip), where N ∼ 10 2 − 10 7 , (see, for example, [22][23][24][25][26][27][28][29][30][31][32][33]) and superfluidity of 4 He in nanodroplets (N ∼ 10 8 − 10 11 ) [34] and porous glasses [35].…”

Matter Waves and Quantum Correlations

“…The 307 ms long expansion time combined with a large collision and hence scattering velocity results in a $6 cm spatial separation between the scattered, correlated atoms. This separation is quite large compared to what has been achieved in recent related BEC experiments based on double-well or two-component systems [14][15][16], trap modulation techniques [17], or spin-changing interactions [18,19]. This makes the BEC collisions ideally suited to quantum-nonlocality tests using ultracold atomic gases and the intrinsic interatomic interactions.…”