Measurement of the Aharonov-Casher phase in an atomic system

Magnetoconductance Anisotropies and Aharonov-Casher Phases

The spin-orbit interaction (SOI) is a key tool for manipulating and functionalizing spin-dependent electron transport. The desired function often depends on the SOI-generated phase that is accumulated by the wave function of an electron as it passes through the device. This phase, known as the Aharonov-Casher phase, therefore depends on both the device geometry and the SOI strength. Here, we propose a method for directly measuring the Aharonov-Casher phase generated in an SOI-active weak link, based on the Aharonov-Casher-phase dependent anisotropy of its magnetoconductance. Specifically, we consider weak links in which the Rashba interaction is caused by an external electric field, but our method is expected to apply also for other forms of the spin-orbit coupling. Measuring this magnetoconductance anisotropy thus allows calibrating Rashba spintronic devices by an external electric field that tunes the spin-orbit interaction and hence the Aharonov-Casher phase.

Spectroscopic Evidence of the Aharonov-Casher Effect in a Cooper Pair Box

We observe the effect of the Aharonov-Casher (AC) interference on the spectrum of a superconducting system containing a symmetric Cooper pair box (CPB) and a large inductance. By varying the charge n_{g} induced on the CPB island, we observe oscillations of the device spectrum with the period Δn_{g}=2e. These oscillations are attributed to the charge-controlled AC interference between the fluxon tunneling processes in the CPB Josephson junctions. The measured phase and charge dependences of the frequencies of the |0⟩→|1⟩ and |0⟩→|2⟩ transitions are in good agreement with our numerical simulations. Almost complete suppression of the single fluxon tunneling due to destructive interference is observed for the charge n_{g}=e(2n+1). The CPB in this regime enables fluxon pairing, which can be used for the development of parity-protected superconducting qubits.

Measurement of the He-McKellar-Wilkens topological phase by atom interferometry and test of its independence with atom velocity

In this Letter, we report a measurement of the He-McKellar-Wilkens (HMW) topological phase by atom interferometry. The experiment is done with our lithium atom interferometer, and in order to suppress the stray effects present in our first experiment, we use optical pumping of the (7)Li atoms in their F=2, m(F)=+2 (or -2) ground state sublevel. In these conditions, the measured phase shift is the sum of the HMW phase and of the Aharonov-Casher phase, which are separated due to their different m(F) dependence. The HMW phase has been measured for different lithium beam velocities and the results are in very good agreement with a phase independent of the atom velocity, as expected for a topological phase.

He-McKellar-Wilkens topological phase in atom interferometry

We report an experimental test of the topological phase predicted by He and McKellar in 1993 and by Wilkens in 1994: this phase, which appears when an electric dipole propagates in a magnetic field, is connected to the Aharonov-Casher effect by electric-magnetic duality. The He-McKellar-Wilkens phase is quite small, at most 27 mrad in our experiment, and this experiment requires the high phase sensitivity of our atom interferometer with spatially separated arms as well as symmetry reversals such as the direction of the electric and magnetic fields. The measured value of the He-McKellar-Wilkens phase differs by 31% from its theoretical value, a difference possibly due to some as yet uncontrolled systematic errors.

Aharonov-Casher and scalar Aharonov-Bohm topological effects

We reexamine the topological and nonlocal natures of the Aharonov-Casher and scalar Aharonov-Bohm phase effects. The underlying U(1) gauge structure is exhibited explicitly. And the conditions for developing topological Aharonov-Casher and scalar Aharonov-Bohm phases are clarified. We analyze the arguments of M. Peshkin and H. J. Lipkin [Phys. Rev. Lett. 74, 2847 (1995)] in detail and show that they are based on the wrong Hamiltonian which yields their conclusion incorrect.

Flux-free conductance modulation in a helical Aharonov--Bohm interferometer

A novel conductance oscillation in a twisted quantum ring composed of a helical atomic configuration is theoretically predicted. The internal torsion of the ring is found to cause a quantum phase shift in the wavefunction that describes the electron's motion along the ring. The resulting conductance oscillation is free from magnetic flux penetrating inside the ring, which is in complete contrast with the case for the ordinary Aharonov-Bohm effect observed in untwisted quantum rings.

Topological phases for composite particles with dynamic properties

We show that, if a given electromagnetic property of a particle is allowed to vary during an evolution where the particle will accrue a topological phase, then it is both the time average and the statistical variance of this property which will affect the observable phenomena. The time average is shown to affect the topological aspect of the phase. This is in addition to a second smaller dynamical phase term, which depends upon only the variance of the changing property. The theory is illustrated in reference to the time dependence of the dipole moment in both the Aharonov-Casher and He-McKellar-Wilkens effects.