Superconducting Quantum Devices 2024
LOCATION
London, Institute of Physics
WHEN
Tues, 18 Jun 2024
James Wills
QUANTUM ENGINEER
James completed his PhD in Physics at the University of Oxford, in the group of Peter Leek. He worked on the design, simulation, and measurement of novel coaxial qubits, specialising in multi-mode coaxial transmons for quantum computing and sensing applications. He joins OQC as a Quantum Engineer, working in the Quantum Research and Development team.
DUAL-RAIL ENCODING OF A FIXED FREQUENCY MULTIMODE TRANSMON QUBIT WITH ANCILLA-FREE ERASURE ERROR DETECTION
11:00 | 18 JUNE, 2024
Amplitude damping errors are a dominant source of error in high performance quantum processors. A promising approach in error-detection are “erasure qubits”, where amplitude damping errors are converted into detectable leakage outside of the computational subspace. Dual-rail encoding has been demonstrated in superconducting quantum devices to show extended coherence above that of the constituent elements, however, these architectures can require the use of an ancillary qubit to perform the erasure error detection.
Here we present a dual-rail encoding within a single fixed-frequency superconducting multimode transmon qubit. The three island, two junction device comprises two transmonlike modes with a detuning of 1.5 GHz, in a coaxial cQED architecture. A resonator on the opposing side of the substrate allows for the dispersive readout of the multimode state of the device, with an error-detected logical state assignment fidelity of above 99%. We demonstrate the utility of the logical encoded qubit as a quantum memory, showing the logical bit-flip and phase-flip error rates are more than one order of magnitude lower than the physical error rates. Finally, we discuss how the error-detected subspace can be used for investigations into the fundamentals of noise and decoherence in fixed-frequency transmon qubits.
Kowsar Shahbazi
SENIOR NANOFABRICATION ENGINEER
Kowsar specialises in the design, fabrication, process development, and characterisation of devices, as well as deep look into the material science that goes behind the device performance. Prior to joining OQC, Kowsar served as a research associate at the University of Bath, and was a Marie Curie ESR in University of Leeds, where she oversaw the design, fabrication, and process optimisation of magnetic thin films and MEMS devices. Her expertise includes process design, nanofabrication, thin film systems, material science and metrology.
INTEGRATION OF THROUGH-SAPPHIRE SUBSTRATE MACHINING WITH SUPERCONDUCTING QUANTUM PROCESSORS
15:30 | 18 JUNE, 2024
We demonstrate the integration of sapphire substrate machining with wafer-scale QPU production. High coherence qubits have been demonstrated on sapphire thanks to its low-loss. In addition, recent advances such as tantalum-on-sapphire as a qubit ground plane material platform have demonstrated coherence times in advance of 0.4 ms. However, unlike silicon, sapphire does not have an equivalent to deep-silicon etch processes to create through-substrate-vias for the purposes of signal routing or integrated mode-mitigation.
Our work integrates sapphire machining with a full QPU nano-fabrication process and we demonstrate high Josephson junction yield as well as compatibility with high-coherence qubits. We present results of our latest 32Q Processor “OQC Toshiko” with integrated through-sapphire-pillars.
