Materials for qubits

Qubits come in many shapes and forms. Some are better developed, some will make it easier to scale up to big quantum processors and some will require less effort to correct errors. One thing they have in common: they will all benefit from materials optimization.

Intense efforts are underway to produce circuits that integrate a technologically relevant number of qubits. Although qubit control in most material systems is by now mature, device variability is one of the main bottlenecks in qubit scalability. How do we characterize and tune millions of qubits? Machine learning might hold the answer.

Superconducting qubits hold great promise for quantum computing, and recently there have been dramatic improvements in both coherence times and the power of quantum processors. This Review explores how the path forward involves balancing circuit complexity and materials perfection, eliminating defects while designing qubits with engineered noise resilience.

Trapped-ion qubits have great potential for quantum computation, but materials improvements are needed. This Review surveys materials opportunities to improve the performance of trapped-ion qubits, from understanding the surface science that leads to electric-field noise to developing methods for building ion traps with integrated optics and electronics.

Defect-based spin qubits offer a versatile platform for creating solid-state quantum devices. This Review is a guide for understanding the properties and applications of current spin defects, and provides a framework for designing, engineering and discovering new qubit candidates

Germanium is a promising material to build quantum components for scalable quantum information processing. This Review examines progress in materials science and devices that has enabled key building blocks for germanium quantum technology, such as hole-spin qubits and superconductor–semiconductor hybrids.

Topological qubits are attractive because of the potential to store quantum information in a topologically protected manner; however, they are challenging to realize. This Review surveys the recent attempts to realize topological qubits out of materials systems that combine superconductivity, spin–orbit coupling and a magnetic field, and surveys both theoretical ideas and experimental results.

An article in Physical Review Applied reports an architecture based on a ring resonator that supports a network of superconducting qubits with enhanced connectivity and negligible crosstalk.

An article in Physical Review Letters reports a formalism enabling the use of a D-Wave quantum annealer to sample the equilibrium ensemble of dense polymer mixtures.

A paper in Nature reports a laser-free method to entangle two trapped-ion qubits that has high fidelity and potential for scalability.