Publications

A 4 : 1 Transmission-Line Impedance Transformer for Broadband Superconducting Circuits, IEEE

We present a 4 : 1 superconducting transmission-line impedance transformer for cryogenic applications. The device transforms 25 Ω in the coplanar waveguide to 6.25 Ω in the microstrip and is designed to operate at 20 mK. Calibrated measurements in a dilution refrigerator demonstrate a -3 dB bandwidth from 1.6 to 13 GHz. In a modified Ruthroff design, a small capacitor is integrated at the input as a direct-current block, making it suitable for biasing and matching to low-impedance active circuits, such as superconducting quantum interference device (SQUID) amplifiers.

A universal quantum gate set for transmon qubits with strong ZZ interactions, arvix.org/org, Cornell University

We describe the hardware, gateware, and software developed at RTX BBN Technologies for dynamic quantum information processing experiments on superconducting qubits. In dynamic experiments, real-time qubit state information is fedback or fedforward within a fraction of the qubits' coherence time to dynamically change the implemented sequence. The hardware presented here covers both control and readout of superconducting qubits. For readout we created a custom signal processing gateware and software stack on commercial hardware to convert pulses in a heterodyne receiver into qubit state assignments with minimal latency, alongside data taking capability. For control, we developed custom hardware with gateware and software for pulse sequencing and steering information distribution that is capable of arbitrary control flow on a fraction superconducting qubit coherence times. Both readout and control platforms make extensive use of FPGAs to enable tailored qubit control systems in a reconfigurable fabric suitable for iterative development.