APS Global Physics Summit presentations
Wednesday March 19
5:36 pm – 5:48 pm
Accelerating resonator spectroscopy using microwave pulses
Presenter: Oscar Gargiulo
The characterization of microwave resonators is an established method to evaluate materials losses to improve the fabrication process for qubit chips. In addition, high quality resonators are essential for reliable qubit readout at low powers. A typical characterization consists of a measurement of the resonator’s quality factor Qint as a function of the number of photons and temperature. Typically, such measurements rely on a vector network analyser (VNA) specifically designed and calibrated to evaluate the scattering matrix parameters of a system. In this article, we explore the potential of employing pulsed instruments as an alternative to speed up resonator characterization. Such instruments can deliver precise microwave pulses with stable timing and phase and are used for the characterization and control of qubits. Despite the intricacies involved in precisely executing the resonator characterization compared to using a VNA, tailoring unique pulses for individual resonators enables us to accelerate the process while maintaining the data quality. We compare the results with those obtained using a VNA and demonstrate that equivalent results can be achieved almost 3 times faster. The resonator quality factor Qint is extracted using a circle fit routine. Average photon number is obtained after calibrating the instruments output powers, cryostat lines and room temperature cables. All the measurements are performed at 100 mK using a kiutra L-Type Rapid cryostat.
Friday March 21
9:48 am – 10:00 am
Large-scale magnetic cooling for quantum computing
Presenter: Steffen Säubert
As quantum computing advances towards large-scale deployment, achieving ultra-low temperatures efficiently and reliably has become paramount. A promising solution is to scale adiabatic demagnetization refrigeration (ADR), a technique capable of reaching millikelvin temperatures without requiring cryogenic liquids, most notably a technology independent of helium-3. We present a significant milestone, achieving sub-30mK temperatures continuously with ADR for the first time, paving the way for future quantum computing platforms. Our primary objective is to enhance critical ADR components, including mechanical and superconducting (SC) heat switches, magnet and cooling media design as well as the exploration of novel refrigerants. These components are essential to improve cooling performance, both in temperature and cooling power, and ensure scalability. This presentation will cover ongoing research and innovative approaches across these domains, drawing on materials science, thermal management, and SC technology to advance ADR systems. By refining these fundamental technologies, ADR offers a scalable solution, positioning magnetic cooling as a vital platform for the next generation of quantum computing.
Friday March 21
10:00 am – 10:12 am
Presenter: Pau Jorba
Accelerating cryogenic testing and characterization of new materials, designs, and fabrication methods for superconducting quantum devices with a fast and easy-to-use ADR-based cryostat
The performance of superconducting qubits and their associated devices must be improved to minimize error rates and improve coherence times. This requires comprehensive testing and characterization of new materials, innovative designs, and novel fabrication methods. The systematic evaluation of these factors is cumbersome due to classic cryogenic solutions having long cooldown times, requiring trained engineers to operate, and relying on helium-3, an increasingly expensive resource.
We present novel cryostats developed for the characterization and operation of quantum devices at sub-Kelvin temperatures, based on adiabatic demagnetization refrigeration. We describe how continuous sub-Kelvin cooling and wide-range temperature control can be achieved by combining multiple ADR units and mechanical thermal switches. We also present a novel sample loader mechanism that allows cooling samples from room temperature to below 100 mK in less than 3 hours, in a fully automated way. Finally, we show how it can be used to study low-temperature characteristics of superconducting films and resonators, with less than 4 hours between successive measurements.
Friday March 21
10:12 am – 10:24 am
Investigation of the stray magnetic field distribution in a magnetic refrigerator as a potential source of noise and decoherence of superconducting qubits
Presenter: Noelia Fernandez
One important aspect to protect the properties of superconducting qubits is the isolation from external magnetic fields. This raises concerns on the suitability of magnetic refrigerators relying on Adiabatic Demagnetization Refrigeration (ADR) for the characterization of superconducting quantum processors.
We investigate the influence of stray magnetic fields on transmon qubits in a Kiutra L-Type Rapid fast characterization cryostat and show that all key qubit properties can be investigated using such an instrument. Foremost, we study the magnetic field distribution inside the cryostat using a 3D fluxgate and compare our results with numerical simulations. Then we investigate T1, T2, and T2-echo on single qubit devices in different shielding scenarios. We consider three different setups: without any magnetic shielding; with cryogenic multilayer shield to minimize ADR contributions; adding dedicated on-puck shields.
We find the absolute magnetic field strength to vary between >50 µT in an unshielded scenario, to <100 nT in a fully shielded. Further, we show that already with an intermediate scale shielding reliable T1 times of up to 40 µs can be achieved. Our results shed light on an avenue to accelerate research with superconducting qubits as well as their characterization at different manufacturing stages, enabled by fast-turnaround cryostats based on magnetic cooling.
APS Global Physics Summit
📅 March 16-21
📍 Anaheim, California