Bloch Oscillating Transistor - a New Quantum Amplifier
Julien Delahayea, Juha Hasselb, Rene Lindella, Mika Sillanpääa, Mikko Paalanena, Heikki Seppäb, Pertti Hakonena
aLow Temperature Laboratory, Helsinki University of Technology, P.O. Box 2200, 02015 HUT, Finland
bVTT Information Technology, Microsensing, P.O. Box 1207, 02044 VTT, Finland
Bloch Oscillating Transistor (BOT) is a novel mesoscopic three terminal device that provides high input impedance ( >> h/e2), large current gain (about 10), and large bandwidth (100 MHz). The operating principle of a BOT utilizes the fact that Zener tunneling up to a higher band will lead to blockade of Cooper-pair tunneling (Bloch oscillation) in a suitably biased Josephson junction. Bloch oscillation is resumed only after the junction has relaxed to the lowest band by quasiparticle tunneling. Thus, by a small quasiparticle control current one is able to control a much larger supercurrent component. We will discuss the basic theory and our first experimental results, indicating that the principle works in practice.
Shot noise in diffusive SNS and SIN junctions
Francois Lefloch, Christian Hoffmann, David Quirion, Marc Sanquer
CEA/Grenoble -DSM/DRFMC/SPSMS, 17 Av. des Martyrs, 38054 Grenoble cedex 9 - France
We studied shot noise in metallic SNS and doped silicon based SIN junctions. In SNS structures, the shot noise is very much enhanced due to incoherent Multiple Andreev Reflections (MAR) which are truncated, at low voltage, by inelastic electron-electron interaction. These experimental results show good agreement with recent semiclassical theory1. In SIN junctions, the zero voltage conductance is increased by coherent MAR (reflectionless tunneling) and we found that the shot noise is double (SI=4eI) below the Thouless energy and equals the full shot noise (SI=2eI) above. We also present conductance measurements which show the transition from zero bias to finite bias anomaly in double-barrier metallic SININ junctions2.
Tunnel Spectroscopy of a small Al particle
Youiti Ootukaa, Teppei Kurosawaa, Akinobu Kandaa, Yuri Pashkinb, Jaw-Shen Tsaib
aInstitute of Physics, University of Tsukuba, Tsukuba 305-8571, Japan
bNEC Fundamental Research Laboratories, Tsukuba 305-8051, Japan
Previously, we (Y.P. and J.S.T.) succeeded in fabricating a lithographically made Al single-electron transistor that showed gate modulation at room temperature (Yu. A. Pashkin, Y. Nakamura, J. S. Tsai, Appl. Phys. Lett. 76 (2000) 2256 ). In this report, we present experimental results of the current-voltage characteristics at very low temperatures. We find a stepwise structure near the threshold voltage, which is attributed to the discrete energy levels in the island. The distribution of level spacing has a tendency that supports the level repulsion effect.
Tunneling Measurement of a Single Quantum Spin
Lev N. Bulaevskii, Gerardo Ortiz
Theoretical Division, Los Alamos National Laboratory, Los Alamos, NM 87545
Measurement of the tunneling current via a molecule or an atom with a localized spin provides information on the orientation of that spin. Such measurement constitutes an example of indirect-consecutive quantum measurement. We show that a strong tunneling current due to the shot noise suppresses the spin dynamics, such as the spin precession in an external magnetic field, and the relaxation due to the environment (quantum Zeno effect). A weak tunneling current preserves the spin precession but the oscillatory component of the current is much weaker than the noise. We propose an experimental setup to observe Zeno effect in a tunneling system and describe how the tunneling current may be used to read a qubit represented by a single quantum spin 1/2.
Manipulation of local nuclear spin polarization in quantum Hall systems
Tomoki Machidaa,b, Tomoyuki Yamazakia, Susumu Komiyamaa,b
aDepartment of Basic Sciences, University of Tokyo, Japan
bSORST-JST, Japan
We demonstrate a new possibility of locally manipulating nuclear spin polarization in integer quantum Hall (IQH) devices. Nuclear spins in a limited area along IQH edge channels (ECs) are dynamically polarized by selectively populating spin-resolved ECs through the hyperfine interaction. Local radio-frequency (RF) magnetic field generated by transmitting RF current through the micro metallic wire fabricated just above the ECs selectively depolarizes nuclear spins in the region below the wire with nuclear magnetic resonance (NMR). The resulting change of the local nuclear spin polarization is detected by a change of Hall resistance. Two equivalent wires fabricated in series along an edge yield NMR signals with different amplitudes, proving the local manipulation of nuclear spins.
Magnetic-field-induced the quantum Hall effect - Hall insulator transition and hopping conductivity in InAs/GaAs quantum dot layers
Vladimir A. Kulbachinskiia, Roman A. Lunina, Vasiliy A. Rogozina, Boris N. Zvonkova, Dmitriy O. Filatova, Anne de Visserb
aLow Temperature Physics Department, Moscow State University, 119899, Moscow, Russia
bVan der Waals-Zeeman Institute, University of Amsterdam, 1018 XE Amsterdam, The Netherlands
We have investigated the temperature dependence of resistance in the temperature range T = 0.07-300 K and in magnetic field up to 35 T in InAs/GaAs quantum dot layers. In samples with relatively high carrier concentration the quantum Hall effect - Hall insulator transition was observed in high magnetic fields. Two-dimensional Mott variable range hopping conductivity has been observed at low temperatures in samples with low carrier concentration. The length of localization correlates very well with the quantum dot cluster size obtained by Atomic Force Microscope.
1C. Hoffmann et al., submitted to Euro. Phys. Jour. B and E.V. Bezuglyi et al., PRB 63(2001)100501
2D. Quirion et al., PRB 65(2002)100508