We propose an atom optics experiment to measure the stability of the quantum kicked rotor under perturbations of the Hamiltonian. We avail ourselves of the theory of Loschmidt echoes, i.e., we consider the overlap of a quantum state evolved in a perturbed and an unperturbed potential. Atom interferometry allows us to determine the overlap integral in amplitude and phase. A numerical analysis of the kicked rotor in various regimes shows that the quantum signatures of specific classical properties can be detected experimentally.
We propose a scheme that allows us to coherently extract cold atoms from a reservoir in a deterministic way. The transfer is achieved by means of radiation pulses coupling two atomic states which are object to different trapping conditions. A particular realization is proposed, where one state has zero magnetic moment and is confined by a dipole trap, whereas the other state with nonvanishing magnetic moment is confined by a steep microtrap potential. We show that in this setup a predetermined number of atoms can be transferred from a reservoir, a Bose-Einstein condensate, into the collective quantum state of the steep trap with high efficiency in the parameter regime of present experiments.
We draw attention to various aspects of number theory emerging in the time evolution of elementary quantum systems with quadratic phases. Such model systems can be realized in actual experiments. Our analysis paves the way to a new, promising and effective method to factorize numbers. IntroductionInterference of waves instead of Newton's light corpuscles --what a revolutionary idea of Thomas Young pronounced in his famous talk at the Royal Society in 1801 [1]. The opposite idea --particles as waves --proposed by Louis de Broglie and cast into the appropriate mathematical form by Erwin Schrö dinger more than 100 years later opened a new realm in atomic physics with more applications today than ever. ''Can a quantum-mechanical description of physical reality be considered complete?" This famous question raised by Albert Einstein, Boris Podolsky and Nathan Rosen in their seminal paper [2] brought out most clearly the importance of entanglement [3] as the basic ingredient of quantum theory. Interference, wave mechanics and entanglement are the three ideas on which Peter Shor could build his factorization algorithm [4] with a polynomial rather than exponential speed. This discovery gave birth to the new field of quantum information [5]. Guided by the same three central ideas we show in the present paper that the time evolution of elementary quantum systems carries intrinsically the tools to factorize numbers [6].Stationary states have played an important role in the development of quantum mechanics. For this reason the time evolution of wave packets has for many years taken a back seat even in textbooks on quantum theory. In this context it is interesting to recall that already in 1927 Kennard [7] studied the time evolution of wave packets in simple potentials [8]. Recently, sophisticated techniques to create short laser pulses have opened a new era for a controlled creation and observation of wave packets in atoms [9], molecules [10] and cavities [11]. Even wave packet dynamics of cold atoms [12] and Bose-Einstein condensates [13] has been observed. These examples illustrate convincingly that today's technology allows to promote this gedankenexperiment of factorization to a real implementation in a quantum system.The use of wave packet dynamics to factorize numbers has been recognized for special examples. Clauser and Dowling [14] uses a N-slit Young interference setup. Hence, the number to be factorized is encoded in the number of slits. The indicator of a factor is the interference pattern on a screen as a function of the wavelength of the light or matter wave. Whenever the intensity across the screen is constant, the appropriately scaled wavelength provides a factor. Similarly, Harter [15] considers the time evolution of a particle in a box. In contrast to these contributions we provide a general framework for factorization and moreover, exhaust the potential of interference by capitalizing on properties of quadratic phase factors.
We present two physical systems which make Gauß sums experimentally accessible. The probability amplitude for a two-photon transition in an appropriate ladder system driven by a chirped laser pulse is determined by a Gauß sum. The autocorrelation function of a quantum rotor is also of the form of a Gauß sum. These examples suggest rules for determining prime factor components on the basis of the properties of Gauß sums. Moreover, we show how Gauß sums are related to the Riemann Zeta function.
We propose two experimentally feasible methods based on atom interferometry to measure the quantum state of the kicked rotor.
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