by Mark Eriksson
The Q-NEXT Materials and Integration (M&I) thrust area focuses on maintaining and enhancing quantum coherence and entanglement in integrated and heterogeneous qubits and quantum devices. M&I research spans the wide breadth of quantum information’s physical implementations, ranging from atomic-scale defects to superconducting qubits and highly integrated systems.
At the truly microscopic scale, M&I investigator Giulia Galli and her University of Chicago team have developed an atomistic understanding of the formation of coherent defect centers in silicon carbide, enabling the theoretical prediction of experimental conditions required for effective synthesis of these qubits, including practical details such as the experimental conditions for stability and activation of the defect centers.
Even at much larger, mesoscopic, length scales, the long coherence of superconducting devices that makes them excellent qubits is still limited in the end by atomic-scale imperfections. Robert McDermott of Applied Materials leads an M&I effort that has improved the T1 relaxation rates of such qubits by dramatically reducing the likelihood that they have short T1 times. Such advances in reducing – and ideally eliminating – even small-likelihood outliers is a challenging yet crucial requirement to successfully integrate large numbers of qubits into quantum processors.
At intermediate length scales, silicon quantum dot qubits are fabricated using processing compatible with highly developed classical CMOS fabrication technology. Together with Intel Corporation, Q-NEXT’s M&I and Quantum Foundry thrust areas have developed a testbed to advance silicon qubits with a particular focus on materials properties and the effects of device fabrication. Together this team recently has identified an important correlation length revealing how quickly silicon qubit properties change as a function of length down a qubit array. The measured correlation length is explained well by the atomic-scale randomness in the silicon-germanium alloy that is at the center of this qubit platform.
Jonathan Marcks (Argonne), Jack Reily (UW-Madison) and Chris Wang (UChicago/Argonne) work in the testbed made possible through the collaboration of Q-NEXT’s M&I and Quantum Foundries thrust areas, Argonne National Laboratory and Intel Corporation. Photo: Argonne National Laboratory/Jason Creps
As these examples all indicate, atomic-level understanding is crucial to qubit development. M&I researcher Danna Freedman (MIT) , in collaboration with Q-NEXT Director David Awschalom (University of Chicago) and M&I theorist Giulia Galli, has taken this fact to a natural conclusion by demonstrating carefully designed molecular color centers in which the position of each atom is known. These centers display emission spanning the range from near infrared through the telecom bands. Their team also has control over the molecular matrix encapsulating the color center and has demonstrated how that matrix can be modified to directly increase quantum coherence times.
Optical transmission of quantum information, especially in the infrared telecom bands, offers the potential to couple to a quantum memory, which is the focus of an M&I project led by Supratik Guha (University of Chicago, Argonne) and Alan Dibos (Argonne). Their team has recently demonstrated the integration of erbium-doped titanium dioxide into nanocavities, achieving a Purcell enhancement of the emission rate by a factor of more than 400.
It is widely believed that practical quantum technologies will continue to be ever more hybrid and heterogeneous in their component parts. By linking researchers across the breadth of Q-NEXT research, M&I team members work on the processing, understanding and integration of qubits and quantum devices. This work brings closer to reality the future vision of truly hybrid quantum information systems that have an impact and performance superior to anything that could be achieved in isolation.