Isolation filters for macroscopic quantum coherence experiment

Abstract

One of the main difficulties in observing quantum coherence (MQC) in rf-SQUID based systems is extremely short coherence times.Quantum coherence in macroscopic system is rapidly destroyed by interaction with the environment. This precludes any MQC experiments from using high-speed data acquisition that allows direct evidence of coherent evolution of linear combination of rf-SQUID eigenstates. In order to perform such experiments, isolation structures that effectively shield MQC experimental elements from small-signal interaction with data acquisition circuitry on chip and at the same time allow large signals such as RSFQ pulses to propagate through. We consider design and simulation of series of Josephson junctions with varied parameters as an example of such isolation filters.

Quantum–classical interface based on single flux quantum digital logic

“…Moreover, little to no effort was made to preserve high quantum coherence with the introduction of a dissipative quantum-classical interface. Subsequent work focused on the thermal budget [53][54][55][56] and electromagnetic compatibility [57][58][59][60] of the SFQ elements, critical considerations for minimizing decoherence. During the European project RSFQubit, a foundry was established at VTT [61] that could provide some unique features required for millikelvin operation of SFQ elements, including critical current densities from 10-30 A/cm 2 , Cu cooling fins for thermalization of shunt resistors [62], and quasiparticle traps.…”

Low-Jc Rapid Single Flux Quantum (RSFQ) Qubit Control Circuit

“…The first proposals of monolithically integrating RSFQ with qubits [1], [2] involved many junctions at large current densities, . Since then, work pertaining to RSFQ engineering at mK temperatures has made thermal budgeting [4]- [7] and electromagnetic compatibility [8], [9] paramount for minimizing decoherence. One conclusion, for monolithic integration, is that RSFQ must be fabricated with a small number of low critical current, , junctions to minimize power dissipation at GHz operational frequency.…”