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Physica C Superconductivity

Operation of SFQ circuits cooled with 4 K closed-cycle refrigerator

Hideo Suzuki, H. Hirano, K. Tanabe

Published Sep 28, 2004• 0 citations
Publisher
DOI
10.1016/j.physc.2004.01.153

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4/spl times/4 single-flux-quantum (SFQ) network switch has been packaged and successfully demonstrated in a hybrid closed-cycle refrigerator (CCR) system at multigigabit data rates. Full operation of the packaged switch, with self-routing of 1-Gb/s data packets, was demonstrated using a 1-GHz address header decode. The switch is packaged on a superconducting multichip module (MCM) mounted on the 4.5-K stage of the CCR. On-chip asynchronous Josephson drivers and cooled GaAs preamplifiers are used to amplify the SFQ outputs of the switch. The maximum operation bandwidth of the switch is currently limited by the asynchronous Josephson driver. New designs of the Josephson drivers, which have demonstrated operation at 10 Gb/s, are expected to enable switch operation at 10 Gb/s. The system is equipped with fiber-optical inputs and high-speed cryogenic photodetectors. The fiber-optic interfaces, RF packaging, and MCM packaging in the CCR system have demonstrated error-free operation at 10 Gb/s.
It is quite beneficial to operate superconducting hot-electron-bolometer (HEB) mixers with a close-cycled 4 Kelvin refrigerator for real applications such as astronomy and atmospheric research. In this paper, a phononcooled NbN HEB mixer (quasioptical type) is thoroughly characterized under such a cooling circumstance. The effects of mechanical vibration, electrical interference, and temperature fluctuation of a two-stage Gifford-McMahon 4 Kelvin refrigerator upon the characteristics of the phononcooled NbN HEB mixer are investigated in particular. Detailed measurement results are presented.
We propose a thermodynamic refrigeration cycle which uses indefinite causal orders to achieve nonclassical cooling. The cycle cools a cold reservoir while consuming purity in a control qubit. We first show that the application to an input state of two identical thermalizing channels of temperature T in an indefinite causal order can result in an output state with a temperature not equal to T. We investigate the properties of the refrigeration cycle and show that thermodynamically, the result is compatible with unitary quantum mechanics in the circuit model but could not be achieved classically. We believe that this cycle could be implemented experimentally using tabletop photonics. Our result suggests the development of a new class of thermodynamic resource theories in which operations are allowed to be performed in an indefinite causal order.