Quantum Information and Measurements

America's future prosperity and security may rely in part on the exotic properties of quantum mechanics. Research on quantum information (QI) seeks to control and exploit these properties, and researchers are already generating "unbreakable" codes for ultra-secure encryption. They may someday build quantum computers that can solve problems in seconds that today’s best supercomputers could not solve in years. This project applies the properties of a macroscopic quantum system, superconductivity, to the development of quantum bits (qubits), quantum circuits, and electrical measurement techniques which are limited only by the laws of quantum physics.

NIST is home to a broad interdisciplinary program in quantum information science, which is exploring multiple implementations of qubits. The efforts include ion-trap quantum computing led by national Medal of Science Winner Dave Wineland, neutral atom quantum computing led by Nobel laureate Bill Philips, and quantum computing incorporating superconducting qubits led by Ray Simmonds of this project. Each of these approaches has associated advantages and challenges. Qubits made from ions and atoms are relatively easy to isolate from environmental influences and thus can maintain their coherence or stable quantum state for longer times. They are, however, more difficult to manipulate, and their properties are dictated by nature. Superconductivity can be used to create "artificial atoms" which are easy to connect to each other and manipulate but are more susceptible to decoherence by interaction with their environment. Work in this project falls into several areas: improving the performance of superconducting qubits by understanding the sources of decoherence and mitigating them, creating and demonstrating the elements of a quantum computer such as quantum memory and a quantum bus, investigating the interaction ("entanglement") of multiple quantum entities, probing at a fundamental level the limits which quantum phenomena place on electrical measurements, and creating instrumentation to approach these limits.

In concrete terms, this work includes theoretical investigations of interactions in qubits and single-charge devices as well as design, fabrication, and characterization of a wide variety of superconducting microdevices. In the qubit arena, we have significantly improved performance by modifying the device structure to reduce or remove dielectric materials (which contain naturally occurring or "rogue" qubits originating in atomic-level defects) from the circuits where possible and to substitute more defect-free materials where they cannot be removed. (Complimentary work on quantum materials for qubits is being performed in the Quantum Magnetic Sensors and Materials Project.) In the instrumentation area, we have designed and demonstrated ultra-low-noise superconducting microwave amplifiers which have the promise to improve microwave measurements in a broad array of applications and potentially push these measurements to the quantum limit.

• Demonstrated coherent quantum state storage and transfer between two phase qubits. Featured on the cover of Nature
  
• Demonstrated DC SQUID microwave amplifier operating in the 7 GHz band with world record gain
  
• Developed vacuum gap capacitors and crossovers and integrated them into superconducting qubits
  
• Developed a resonator technique for evaluating qubit materials which allows rapid screen of candidate materials and fabrication methods
  
• Performed seminal work on the role of quasiparticle poisoning in superconducting circuits which has had a major effect in redirection of qubit development