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arXiv:1410.5451 · Europhysics Letters (EPL)

Toward a test of angular-momentum coherence in a twin-atom interferometer

Carlos R. de Carvalho, Ginette Jalbert, François Impens, Jacques Robert, Aline Medina, Fábio Zappa, N. V. de Castro Faria

Published Jun 1, 2015• 4 citations
arXivHTMLPDF

Abstract

We present a scheme well suited to investigate quantitatively the angular-momentum coherence of molecular fragments. Assuming that the dissociated molecule has a null total angular-momentum, we investigate the propagation of the corresponding atomic fragments in the apparatus. We show that the envisioned interferometer enables one to distinguish unambiguously a spin-coherent from a spin-incoherent dissociation, as well as to estimate the purity of the angular-momentum density matrix associated with the fragments. This setup, which may be seen as an atomic analogue of a twin-photon interferometer, can be used to investigate the suitability of molecule dissociation processes —such as the metastable hydrogen atoms H(2 2 S )-H(2 2 S ) dissociation— for coherent twin-atom optics.

DOI
10.1209/0295-5075/110/50001

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We present a scheme well suited to investigate quantitatively the angular-momentum coherence of molecular fragments. Assuming that the dissociated molecule has a null total angular-momentum, we investigate the propagation of the corresponding atomic fragments in the apparatus. We show that the envisioned interferometer enables one to distinguish unambiguously a spin-coherent from a spin-incoherent dissociation, as well as to estimate the purity of the angular-momentum density matrix associated with the fragments. This setup, which may be seen as an atomic analogue of a twin-photon interferometer, can be used to investigate the suitability of molecule dissociation processes —such as the metastable hydrogen atoms H(2 2 S )-H(2 2 S ) dissociation— for coherent twin-atom optics.
We propose to implement a sub-shot-noise matter-wave interferometer via the stimulated dissociation of a molecular Bose-Einstein condensate and study the collisional loss of atom-molecule coherence during its phase-acquisition time. The obtained nnn-atom states are two-atom [SU(1,1)] coherent states with number variance $\ensuremath{\Delta}n\ensuremath{\propto}n$ compared to $\ensuremath{\Delta}n\ensuremath{\propto}\sqrt{n}$ for the spin [SU(2)] coherent states formed by coherent splitting of an atomic condensate. Consequently, the Lorentzian atom-molecule phase diffusion is faster than the Gaussian phase diffusion between separated atomic condensates by a n\sqrt{n}n​ factor.
We show that two-particle interferences can be used to probe the nuclear motion in a doubly excited hydrogen molecule. The dissociation of molecular hydrogen by electron impact involves several decay channels, associated with different molecular rotational states, which produce quantum interferences in the detection of the atomic fragments. Thanks to the correlations between the angular momentum and the vibrational states of the molecule, the fragments arising from each dissociation channel carry out a phase shift which is a signature of the molecule rotation. These phase shifts, which cannot be observed in a single-atom detection scheme, may be witnessed under realistic experimental conditions in a time-of-flight coincidence measurement. We analyze the interferences arising from the two lowest-energy rotational states of a parahydrogen molecule. Our result shows the relevance of two-fragment correlations to track the molecular rotation.
We report the realization of a hydrogen atom interferometer experiment using light as the atomic beam splitter. The wave packets of hydrogen atoms excited to the metastable 2 S state are coherently split up and later recombined with the help of intense nanosecond light pulses. The pulses are generated by a novel phase-coherent source. These experiments can be seen as a step towards a precision measurement of the recoil energy of a hydrogen atom when absorbing a photon and thus of ℏ/ m hydrogen .
It is well established now that light carries both spin and orbital angular momentum which are associated with circular polarisation and helical phase fronts. Orbital angular momentum degrees of freedom recently have been used frequently in quantum information processing as their states are described by vectors in a higher-dimensional Hilbert space which enhances the possibility of realising superior quantum information protocols. On the other hand, quantum coherence, which arises from the superposition principle, is a distinct feature of quantum mechanics that cannot be satisfactorily described by classical physics. Coherence is also identified as essential ingredient for applications of quantum information, computation, and quantum thermodynamics. Three research projects, with their related background information, are presented in this thesis. In the first one, we design a linear optical system to transform the maximally entangled state of a down-converted photon pair into a genuine entangled χ-type state, as this class of genuine entangled states has been showed to have many interesting entanglement properties and can be employed in several quantum information protocols. In the second project, we study the mechanism of angular momentum transfer from light to a dielectric medium when it undergoes total internal reflection. The result shows that the torque associated with angular momentum transfer appears shortly, when the light pulse hits the interface. Finally, we study quantum coherence transfer from a coherence resource initialised in a coherence state to an atomic state by the Jaynes-Cummings model, and we compare it to the coherent operation that uses a resource prepared in a ladder state described by Åberg’s model. We found that a resource in a coherent state is more robust against failures.
We propose a method for producing entangled spin and orbital states in pairs of atoms resulting from the dissociation of diatomic molecules. The method employs the interference between a one-photon and a two-photon process to break the backward-forward symmetry of the dissociation processes. The spin entanglement of distant atom pairs makes use of excited spin-orbit-coupled (molecular) intermediate states. When the dissociating molecules are confined to a one-dimensional optical lattice, the method can be used to generate long sequences of (spin- and orbit-) entangled pairs of atoms.