Skip to main content
U.S. flag

An official website of the United States government

Official websites use .gov
A .gov website belongs to an official government organization in the United States.

Secure .gov websites use HTTPS
A lock ( ) or https:// means you’ve safely connected to the .gov website. Share sensitive information only on official, secure websites.


The Boulder Cryogenic Quantum Testbed (BCQT) Project implements, develops and openly disseminates standard protocols to reproducibly measure the performance characteristics of superconducting microwave resonators used in quantum computing circuits, especially at millikelvin temperatures and single photon powers.


Boulder Cryogenic Quantum Testbed

The BCQT serves as a resource to academic and industry quantum research groups for measurement of superconducting microwave resonators in a well-characterized cryogenic environment using traceable, open-source methods developed in broad consultation with companies, universities, and NIST.

This project aims to improve the accuracy, precision, and reproducibility of performance measurements of superconducting microwave resonators, especially for materials loss investigations and ultralow powers and millikelvin temperatures. This work includes the study of asymmetric resonance fitting, cryogenic calibration, high-throughput measurement techniques, probing of two-level systems, understanding quasiparticle effects, and resonator device design, among others.

Residing in the McRae Lab in CU Boulder's Engineering Center (ECEE 155), the Boulder Cryogenic Quantum Testbed is a joint initiative of NIST and the University of Colorado Boulder.

parallel-plate capacitor
Micrographs of a parallel-plate capacitor (top left), a lumped element resonator (bottom left), and a coplanar waveguide resonator (right). These devices are leveraged to extract qubit material losses from their ultralow power, ultralow temperature microwave behavior.

Current Research Projects and Interests:

  • Accurate and reproducible materials loss measurements for superconducting qubits
  • Open-source data acquisition and analysis codebase for superconducting microwave resonators
  • Superconducting qubit and resonator noise characterization
  • Two-level-system spectroscopy
  • Linking superconducting device performance to microscopic loss channels such as two-level systems and quasiparticles
  • Performance of microwave packaging
  • High-throughput resonator measurement at single photon powers and millikelvin temperatures
  • Three-dimensional superconducting cavities for bulk dielectric measurements
  • Analysis of asymmetric resonances

Selected Publications

C. J. Kopas, E. Lachman, C. R. H. McRae, Y. Mohan, J. Y. Mutus, A. Nersisyan, and A. Poudel, Simple Coplanar Waveguide Resonator Mask Targeting Metal-Substrate Interface, arXiv:2204.07202.

H. Wang et al., Cryogenic Single-Port Calibration for Superconducting Microwave Resonator Measurements, Quantum Science and Technology 6, (2021).

C. R. H. McRae, G. M. Stiehl, H. Wang, S. X. Lin, S. A. Caldwell, D. P. Pappas, J. Mutus, and J. Combes, Reproducible Coherence Characterization of Superconducting Quantum Devices, Applied Physics Letters 119, (2021).

C. R. H. McRae, H. Wang, J. Gao, M. Vissers, T. Brecht, A. Dunsworth, D. Pappas, and J. Mutus, Materials Loss Measurements Using Superconducting Microwave Resonators, 091101, (2020).

C. R. H. McRae, A. McFadden, R. Zhao, H. Wang, J. L. Long, T. Zhao, S. Park, M. Bal, C. J. Palmstrøm, and D. P. Pappas, Dielectric Loss in Epitaxial Al/GaAs/Al Trilayers for Superconducting Circuits, 1 (2020).

Major Accomplishments

FormFactor dilution refrigerator
Photograph of the coldest four stages of the FormFactor dilution refrigerator used at the Boulder Cryogenic Quantum Testbed.

Millikelvin microwave loss measurement platform in support of the quantum computing industry

The Boulder Cryogenic Quantum Testbed (BCQT) project has developed experimental capability for performing (relatively) high-throughput, accurate measurements of superconducting microwave loss down to single photon powers and millikelvin temperatures. Towards this end, this project developed data-based cryogenic calibration methods and open-source resonator data acquisition and analysis toolkits. The BCQT measurement platform is available to address the significant microwave loss measurement needs of the growing quantum computing industry.

Created April 25, 2023, Updated October 18, 2023