Two-phase 50 GHz on-chip long Josephson junction clock source

Abstract

On-chip, high-frequency clock sources are essential for the future development of superconductor digital circuits and systems. We have developed clock sources for rapid single flux quantum (RSFQ) digital circuits using high-quality long Josephson junction (LJJ) resonant oscillators that offer extremely low jitter. To meet the requirement for time-interleaved clock signals of complementary phase, two-phase 30 and 50 GHz clock sources using LJJ's have been developed with both linear and annular geometry. Unperturbed by reflections from boundaries and collisions among the fluxons (flux quanta), the annular LJJ oscillator has demonstrated superior stability and higher quality factor (10 6) than the linear LJJ oscillator. The LJJ oscillator with linear geometry is easier to interface with RSFQ circuitry since it has well-defined boundaries at either end, facilitating a two-phase clock source. On the other hand, multiple clock phases may be derived from an annular LJJ oscillator by connecting interface circuitry at various points around the circular junction, if the interface circuitry does not interfere with the fluxon(s) in the annular junction. Experimental results for two-phase RSFQ clock sources based on linear and annular LJJ oscillators are presented. Index Terms-Long Josephson junction, on-chip high frequency clock source, superconductor digital electronics.

Sub-nanosecond operations on superconducting quantum register based on Ramsey patterns

“…Thus, the proposed schematic provides a robust solution for the manipulation of a qubit's states at the sub-nanosecond timescale. In this case, the part of the device coupled to the qubit is similar to solutions well known from the literature [59][60][61][62][63]. For the typical parameters of the system under consideration here and its connection with the control line, we obtain 1… 10 mΦ 0 of the flux coupled to the qubit when performing a simple operation.…”

“…We propose a notional engineering solution for the transformation of fluxon pulses into the required unipolar pulses with sharp fronts and independently adjustable amplitude and duration. This makes it possible to control the quantum states of the flux qubit (which once again attracted the attention of researchers [62]) with a fidelity of more than 99% on a subnanosecond timescale. The clear consequence of the proposed concept may be the acceleration of single and multiple-qubit gates that are necessary to obtain new fundamental and applied results using Noisy Intermediate-scale Quantum simulators [64][65][66][67][68].…”

Verification of stable operation of rapid single flux quantum devices with frequency-dependent dissipation

“…For example, the device described here could readily be driven at frequencies up to about 10 GHz. However, to utilise the full potential of integrated control one could eventually apply integrated clock sources [18] instead of an external clock signal such as I in here.…”

Frequency synchronization of single flux quantum oscillators

“…This phenomenon could possibly stabilize the operation of SFQ circuits that are driven by non-optimal bias currents. The frequency synchronization can be applied to any on-chip SFQ clock source, such as single Josephson junction-based SFQ oscillators [32,33] and long Josephson junction oscillators [34,35].…”