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Register a new userQuantum mechanical complementarity probed in a closed-loop Aharonov-Bohm interferometer
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According to Bohrs complementarity principle, a particle possesses wave-like properties only when the different paths the particle may take are indistinguishable. In a canonical example of a two-path interferometer with a which-path detector, observation of interference and obtaining which-path information are mutually exclusive. Such duality has been demonstrated in optics with a pair of correlated photons and in solid-state devices with phase-coherent electrons. In the latter case, which-path information was provided by a charge detector embedded near one path of a two-path electron interferometer. Note that suppression of interference can always be understood either as obtaining path information or as unavoidable back action by the detector. The present study reports on dephasing of an Aharonov-Bohm (AB) ring interferometer via a coupled charge detector adjacent to the ring. In contrast to the two-path interferometer, charge detection in the ring does not always provide path information. Indeed, we found that the interference was suppressed only when path information could be acquired, even if only in principle. This demonstrates that dephasing does not always take place by coupling the `environment to the interfering particle: path information of the particle must be available too. Moreover, this is valid regardless of the strength of environment-interferometer coupling, which refutes the general notion of the effect of strong interaction with the environment. In other words, it verifies that an acquisition of which-path information is more fundamental than the back-action in understanding quantum mechanical complementarity.
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One of the points at issue with closed-loop-type interferometers is beating in the Aharonov-Bohm (AB) oscillations. Recent observations suggest the possibility that the beating results from the Berry-phase pickup by the conducting electrons in materials with the strong spin-orbit interaction (SOI). In this study, we also observed beats in the AB oscillations in a gate-defined closed-loop interferometer fabricated on a GaAs/AlGaAs two-dimensional electron-gas heterostructure. Since this heterostructure has very small SOI, the picture of the Berry-phase pickup is ruled out. The observation of beats in this study, with the controllability of forming a single transverse subband mode in both arms of our gate-defined interferometer, also rules out the often-claimed multiple transverse subband effect. It is observed that nodes of the beats with an h/2e period exhibit a parabolic distribution for varying the side gate. These results are shown to be well interpreted, without resorting to the SOI effect, by the existence of two-dimensional multiple longitudinal modes in a single transverse subband. The Fourier spectrum of measured conductance, despite showing multiple h/e peaks with the magnetic-field dependence that are very similar to that from strong-SOI materials, can also be interpreted as the two-dimensional multiple-longitudinal-modes effect.
Majorana zero modes are leading candidates for topological quantum computation due to non-local qubit encoding and non-abelian exchange statistics. Spatially separated Majorana modes are expected to allow phase-coherent single-electron transport through a topological superconducting island via a mechanism referred to as teleportation. Here we experimentally investigate such a system by patterning an elongated epitaxial InAs-Al island embedded in an Aharonov-Bohm interferometer. With increasing parallel magnetic field, a discrete sub-gap state in the island is lowered to zero energy yielding persistent 1e-periodic Coulomb blockade conductance peaks (e is the elementary charge). In this condition, conductance through the interferometer is observed to oscillate in a perpendicular magnetic field with a flux period of h/e (h is Plancks constant), indicating coherent transport of single electrons through the islands, a signature of electron teleportation via Majorana modes, could also be observed, suggesting additional non-Majorana mechanisms for 1e transport through these moderately short wires.
We address the quantum dot phase measurement problem in an open Aharonov-Bohm interferometer, assuming multiple transport channels. In such a case, the quantum dot is characterized by more than one intrinsic phase for the electrons transmission. It is shown that the phase which would be extracted by the usual experimental method (i.e. by monitoring the shift of the Aharonov-Bohm oscillations, as in Schuster {it et al.}, Nature {bf 385}, 417 (1997)) does not coincide with any of the dot intrinsic phases, but is a combination of them. The formula of the measured phase is given. The particular case of a quantum dot containing a $S=1/2$ spin is discussed and variations of the measured phase with less than $pi$ are found, as a consequence of the multichannel transport.
Electron transport through two parallel quantum dots is a kind of solid-state realization of double-path interference. We demonstrate that the inter-dot Coulomb correlation and quantum coherence would result in strong current fluctuations with a divergent Fano factor at zero frequency. We also provide physical interpretation for this surprising result, which displays its generic feature and allows us to recover this phenomenon in more complicated systems.
We investigate a Fabry-Perot interferometer in the integer Hall regime in which only one edge channel is transmitted and n channels are trapped into the interferometer loop. Addressing recent experimental observations, we assume that Coulomb blockade effects are completely suppressed due to screening, while keeping track of a residual strong short range electron-electron interaction between the co-propagating edge channels trapped into the interferometer loop. This kind of interaction can be completely described in the framework of the edge-magnetoplasmon scattering matrix theory allowing us to evaluate the backscattering current and the associated differential conductance as a function of the bias voltage. The remarkable features of these quantities are discussed as a function of the number of trapped channels. The developed formalism reveals very general and provides also a simple way to model the experimentally relevant geometry in which some of the trapped channels are absorbed into an Ohmic contact, leading to energy dissipation.
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