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Japanese Journal of Applied Physics

Observation of Coulomb Blockade and Interference Using a Carbon Nanotube Tip

Hitoshi Nejo, Pavel S. Dorozhkin, Hirokazu Hori

Published Jul 30, 2003• 0 citations
Publisher

Abstract

Using a carbon nanotube (CNT) bundle tip as a field emitter, we have observed both Coulomb blockade and interference fringes in consecutive measurements. When Coulomb blockade is observed, decoherence of the electron wave occurs. This was observed using a double-tunnel junction consisting of a CNT tip and a CNT sample. When the CNT sample was projected onto a screen by an electron wave from the CNT tip, interference fringes were observed. This shows that the electron is first observed at the central electrode as a Coulomb blockade, next it is observed at the CNT sample as current when the electron leaves from the central electrode (the CNT tip) and finally observed as fringes passing through the CNT sample. These results show that the system's wave function cannot be written as a direct product of independent substates.

DOI
10.1143/jjap.42.4743

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Using a carbon nanotube (CNT) bundle tip as a field emitter, we have observed both Coulomb blockade and interference fringes in consecutive measurements. When Coulomb blockade is observed, decoherence of the electron wave occurs. This was observed using a double-tunnel junction consisting of a CNT tip and a CNT sample. When the CNT sample was projected onto a screen by an electron wave from the CNT tip, interference fringes were observed. This shows that the electron is first observed at the central electrode as a Coulomb blockade, next it is observed at the CNT sample as current when the electron leaves from the central electrode (the CNT tip) and finally observed as fringes passing through the CNT sample. These results show that the system's wave function cannot be written as a direct product of independent substates.
We study quantum optical properties of the single-walled carbon nanotube (SWCNT) by introducing the effective interaction between the quantized electromagnetic field and the confined electrons in the SWCNT. Our purpose is to explore the quantum natures of electron transport in the SWCNT by probing its various quantum optical properties relevant to quantum coherence, such as the interference of the scattered and emitted photons, and the bunching and anti-bunching of photons which are characterized by the higher order coherence functions. In the strong field limit, we study the interband Rabi oscillation of electrons driven by a classical light. We also investigate the possible lasing mechanism in superradiation of coherent electrons in a SWCNT driven by a light pump or electron injection, which generate electron population inversion in the higher energy-band of SWCNT.
We propose a device which implements a solid-state nanostructured electron entangler. It consists of a single-walled carbon nanotube connected at both ends to normal state electrodes and coupled in its middle part to a superconducting nanowire. Such a device acts as an electronic beam splitter for correlated electrons originating from the superconductor. We first show that it can be used to detect positive (bosonic-like) noise correlations in a fermionic system. Furthermore, it provides a source for entangled electrons in the two arms of the splitter. To generate entangled electron states, we propose two kinds of set-up based either on spin or energy filters. They respectively consist of ferromagnetic pads and of a system of electrostatic gates which define quantum dots. The fabrication of this device would require state-of-the-art nanofabrication techniques, carbon nanotube synthesis and integration, as well as atomic force microscopy imaging and manipulation.
Understanding how fermionic exchange and Coulomb repulsion jointly shape two-electron correlations is essential for identifying genuine quantum signatures in multi-electron interference experiments. To address this interplay, we investigate Hanbury Brown and Twiss interference of two electrons generated by two independent needle-tip emitters within a full quantum-mechanical framework. In the absence of Coulomb interaction, the approach reproduces the results previously obtained within a quantum path formalism. For Coulomb-interacting electrons, we predict characteristic features absent in a semiclassical description: a pronounced Coulomb-dominated suppression region as well as Coulomb-induced phase offsets and fringe shifts. At the same time, outside of the Coulomb-dominated region, the spatial oscillation frequency is essentially governed by fermionic exchange symmetry. Our results establish quantitative parameter regimes for disentangling Coulomb interaction from fermionic exchange symmetry in such experiments.
Abstract This work describes the study of a superconducting quantum interference device (SQUID) with single‐walled carbon nanotube (CNT) Josephson junctions. Quantum confinement in each junction induces a discrete quantum dot (QD) energy level structure, which can be controlled with two lateral electrostatic gates. The gates are also used to directly tune the quantum phase interference of the Cooper pairs circulating in the SQUID ring. Optimal modulation of the switching current with magnetic flux is achieved when both QD junctions are in the ‘on’ or ‘off’ state. In particular, the SQUID design establishes that these CNT Josephson junctions can be used as gate‐controlled π junctions. Besides, the CNT‐SQUIDs are sensitive local magnetometers, which are very promising for the study of magnetization reversal of an individual magnetic particle or molecule placed on one of the two CNT Josephson junctions. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
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Electron double-slit experiments, the essence of quantum mechanical “wave/particle duality”, have been extensively and continuously studied because their unrealistic interpretations have attracted many researchers. Here, we discuss recent sophisticated V-shaped double-slit experiments to elucidate electron-path information, i.e., which slit electrons pass through, which path they pursue, and where they arrive and interfere on the image plane. In a transmission electron microscope, an optically zero-propagation distance condition was realized, where the double-slit position was imaged just on the detector plane. Interference fringes composed of dot images were controlled by using two electron biprisms. Using a V-shaped double slit, we confirmed that it is possible to observe interference fringes only when the path information of individual electrons is not available. Furthermore, we studied how the interference fringes would shift their detected positions when electron wave phases were modulated before illumination to the double slit. Phase shifts were generated by tilting electron beams. We confirmed that each single electron as a wave changed its phase even when it traveled alone inside the microscope.