| Zugriffsnummer | 15768 |
| Dokumenttyp | Konferenzartikel |
| Sprache | Englisch |
| Titel | Frequency-locked current of Cooper pairs in superconducting single electron transistor with Ohmic resistor |
| Autor(in); Institution |
Lotkhov, Sergey V.; 2.42, Metallische Strukturen, PTB-Braunschweig
Bogoslovsky, Sergey A.; Moscow State University, Laboratory of Cryoelectronics, Moscow, RUSSIA
Zorin, Alexander B.; 2.42, Metallische Strukturen, PTB-Braunschweig
Niemeyer, Jürgen; 2.4, Quantenelektronik, PTB-Braunschweig
|
| Quelle/Jahr | International Workshop on Superconducting Nano-Electronics Devices : SNED proceedings, Naples, Italy, May 28 - June 1, 2001:(2002), 105 - 114 |
| Herausgeber(in) |
Pekola, Jukka; University of Jyväskylä, FINLAND
|
| ISBN | 0-306-47266-X |
| Verlag | New York [u.a.]: Kluwer Acad./Plenum Publishers |
| Konferenzangaben | International Workshop on Superconducting Nano-Electronics Devices ; SNED, Naples, 28, May - 1, June, 2001, Italy |
| Freie Schlagworte | Josephson junctions ; single Cooper pair tunneling ; macroscopic quantum coherence |
| Zusammenfassung | In the last few years, the objects exhibiting quantum-mechanical behaviour on the macroscopic level have been given a renewed interest of researchers with a view to their possible application in quantum computing. One of the most promising implementations of such objects is in systems with small Josephson junctions, which can be fabricated by the methods of planar nanotechnology. The macroscopic charge motion in such systems is related to the specific energy diagram, which, due to the interplay of the Josephson and the charging effects, appears as a set of energy bands of the Bloch-type. In the case EJ < < EC, where EJ and EC are the typical charging and Josephson energies respectively, the 2e-periodic pattern of the neighbouring bands is featured by the regions of avoided crossings in the points of single Cooper pair resonance. The adiabatically slow motion across a point of resonance along the upper band, in the limit of vanishing damping, does not lead to downward band switching, which results in an elastic and, therefore, reversible transfer of a Cooper pair across one of the tunnel junctions. On the contrary, finite damping introduced by a dissipative environment facilitates the inter-band transitions, namely, relaxation to the lower state, which occurs without charge transfer. This process is irreversible: the opposite sweep does not lead to back switching into the upper band, but results in sliding along the lower band and elastic transfer of a Cooper pair. This effect of a dissipative environment makes it possible to realize the controlled transfer of single Cooper pairs in the simplest system of two junctions with the gate (Bloch transistor) embedded in a dissipative environment realized as an ohmic resistor connected in series. In this paper we report on the first experimental observation of the dc current of Cooper pairs generated with the help of a harmonic rf signal applied to the gate. The cycling trajectory was chosen in such a way that the points of resonance were met four times per cycle, resulting in only two co-directed tunnel events, one per junction. The other two tunneling events, which would have taken place if there was no dissipation and which would have reset to zero the total current, do not occur. Instead, the interband transition (relaxation) enhanced by the ohmic environment takes place. As a result, one Cooper-pair is transferred through the transistor in one cycle. In our experiment, a 7 μm-long stripline of Cr, R = 40 kΩ was connected in series to the Bloch transistor composed of two small Al Josephson junctions with CT = 160 aF and RT = 35 kΩ each and supplied with the gate electrode with Cg = 11 aF. As can be inferred from the device parameter, the characteristic energies were EJ = 16 μeV and EC =250 μeV (i.e. EJ = 6.5%EC), both much larger than the thermal energy at kbT = 0.86 μeV (at T = 10 mK). As they were suppressed by the resistor, no JQP peaks were observed on the I - V curve without rf signal; neither non-zero critical current nor the finite sub-gap leakage currents were registered. The rf drive of frequency f of several MHz and amplitude VA = e/Cg = 14 mV applied to the gate gave rise to the current plateaus, their height approaching the expected levels I = 2ef. The deviations of the plateaus from the theoretical levels can be explained if the accompanying processes (Landau-Zener tunneling, quasiparticle tunneling, cycle missing, etc.) are taken into account. |
Zitierung
Lotkhov, S. V., Bogoslovsky, S. A., Zorin, A. B., & Niemeyer, J. (2002). Frequency-locked current of Cooper pairs in superconducting single electron transistor with Ohmic resistor. International Workshop on Superconducting Nano-Electronics Devices ; SNED, Naples, 28, May - 1, June, 2001, Italy.