# Dresden 2006 – wissenschaftliches Programm

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# TT: Tiefe Temperaturen

## TT 1: Superconductivity: Tunnelling, Josephson Junctions, SQUIDs

### TT 1.4: Vortrag

### Montag, 27. März 2006, 10:15–10:30, HSZ 02

**Frozen-flux-quanta phase shifter for digital Josephson circuits** — •Dmitry Balashov^{1}, M. Khabipov^{1}, D. Hagedorn^{1}, A. B. Zorin^{1}, F.-Im. Buchholz^{1}, J. Niemeyer^{1}, B. Dimov^{2}, Th. Ortlepp^{2}, and F. H. Uhlmann^{2} — ^{1}Physikalisch-Technische Bundesanstalt, 38116 Braunschweig, Germany — ^{2}Technische Universität Ilmenau, 98684 Ilmenau, Germany

Superconducting Rapid Single Flux Quantum (RSFQ) digital circuits are very
promising for integration with Josephson qubits of different types. The basic
quantization condition of each RSFQ cell is given by *LI*_{c}>Φ_{0} (*L* is
the loop inductance and Φ_{0} ≈ 2.07 mV·ps is the single
flux quantum). For qubit applications, the critical current *I*_{c} of the RSFQ
circuits should be set to about several µA, which, in turn, requires large
geometrical inductance of the loop to ensure a certain phase shift inside or
between the cells. The replacement of large inductances by the novel passive phase shifting elements based on small integer numbers of flux quanta frozen in the superconducting loops provides the well-defined phase shift. We report on the experimental verification of operation of such compact passive phase shifter
elements realised in standard niobium SIS-trilayer technology for two different
critical current densities: *j*_{c} = 100 A/cm^{2} (*I*_{c}^{min} = 10
µA), and *j*_{c} = 1 kA/cm^{2} (*I*_{c}^{min} = 125 µA). The
flux quanta injection to the phase shifter loops was managed by feeding proper
current into specially designed control lines.

This work is supported by DFG (NI253/7-1, UH53/6-1) and the EU (RSFQubit).