Toward optically driven electrical quantum metrology

We use a mode-locked laser to drive Josephson junction arrays (JJA) [1]. Our method is promising for driving, e.g., Josephson Arbitrary Waveform Synthesizers (JAWS) or single flux quantum (SFQ) logic. Both can benefit from a fast optical data bus that minimizes the heat load into the cryostat compared to conventional electrical cabling. Our mode-locked laser generates a pattern of optical pulses that we convert into electrical ones with a photodiode at a cryogenic temperature. Under suitable operating conditions, each electrical pulse yields a quantized voltage pulse in all of the Josephson junctions of the array. We operate our mode-locked laser at a modest pulse frequency of about 2-3 GHz and use time division multiplexing (TDM) to yield a multiplied pulse frequency for driving the JJA. We show that the measurement of DC voltage for a JJA driven by double pulses with a varied time delay between them allows to study electrical transmission line effects in the system consisting of the photodiode and the JJA. Improvements in cryogenic optical packaging enable more ideal transmission lines, which is important for our future goal to increase the pulse frequency of JAWS.