A quantum computer is a computer that exploits quantum mechanical phenomena. At small scales, physical matter exhibits properties of both particles and waves, and quantum computing leverages this behavior using specialized hardware. Classical physics cannot explain the operation of these quantum devices, and a scalable quantum computer could perform some calculations exponentially faster than any modern "classical" computer. In particular, a large-scale quantum computer could break widely used encryption schemes and aid physicists in performing physical simulations; however, the current state of the art is largely experimental and impractical.
In electronics, rapid single flux quantum (RSFQ) is a digital electronic device that uses superconducting devices, namely Josephson junctions, to process digital signals. In RSFQ logic, information is stored in the form of magnetic flux quanta and transferred in the form of Single Flux Quantum (SFQ) voltage pulses. RSFQ is one family of superconducting or SFQ logic. Others include Reciprocal Quantum Logic (RQL), ERSFQ – energy-efficient RSFQ version that does not use bias resistors, etc. Josephson junctions are the active elements for RSFQ electronics, just as transistors are the active elements for semiconductor electronics. RSFQ is a classical digital, not quantum computing, technology.
In quantum computing, a charge qubit is a qubit whose basis states are charge states. In superconducting quantum computing, a charge qubit is formed by a tiny superconducting island coupled by a Josephson junction to a superconducting reservoir. The state of the qubit is determined by the number of Cooper pairs which have tunneled across the junction. In contrast with the charge state of an atomic or molecular ion, the charge states of such an "island" involve a macroscopic number of conduction electrons of the island. The quantum superposition of charge states can be achieved by tuning the gate voltage U that controls the chemical potential of the island. The charge qubit is typically read-out by electrostatically coupling the island to an extremely sensitive electrometer such as the radio-frequency single-electron transistor.
Superconducting quantum computing is a branch of solid state quantum computing that implements superconducting electronic circuits using superconducting qubits as artificial atoms, or quantum dots. For superconducting qubits, the two logic states are the ground state and the excited state, denoted respectively. Research in superconducting quantum computing is conducted by companies such as Google, IBM, IMEC, BBN Technologies, Rigetti, and Intel. Many recently developed QPUs utilize superconducting architecture.
In quantum computing, more specifically in superconducting quantum computing, flux qubits are micrometer sized loops of superconducting metal that is interrupted by a number of Josephson junctions. These devices function as quantum bits. The flux qubit was first proposed by Terry P. Orlando et al. at MIT in 1999 and fabricated shortly thereafter. During fabrication, the Josephson junction parameters are engineered so that a persistent current will flow continuously when an external magnetic flux is applied. Only an integer number of flux quanta are allowed to penetrate the superconducting ring, resulting in clockwise or counter-clockwise mesoscopic supercurrents in the loop to compensate a non-integer external flux bias. When the applied flux through the loop area is close to a half integer number of flux quanta, the two lowest energy eigenstates of the loop will be a quantum superposition of the clockwise and counter-clockwise currents. The two lowest energy eigenstates differ only by the relative quantum phase between the composing current-direction states. Higher energy eigenstates correspond to much larger (macroscopic) persistent currents, that induce an additional flux quantum to the qubit loop, thus are well separated energetically from the lowest two eigenstates. This separation, known as the "qubit non linearity" criteria, allows operations with the two lowest eigenstates only, effectively creating a two level system. Usually, the two lowest eigenstates will serve as the computational basis for the logical qubit.
Alexander Rudolf Hamilton is with the School of Physics at the University of New South Wales (UNSW). He is notable in the area of experimental condensed matter physics, particularly semiconductor nanofabrication and the study of quantum effects in nanometer scale electronic devices at ultra-low temperatures.
In quantum computing, and more specifically in superconducting quantum computing, the phase qubit is a superconducting device based on the superconductor–insulator–superconductor (SIS) Josephson junction, designed to operate as a quantum bit, or qubit.
Charles Tahan is a U.S. physicist specializing in condensed matter physics and quantum information science and technology. He currently serves as the Assistant Director for Quantum Information Science (QIS) and the Director of the National Quantum Coordination Office (NQCO) within the White House Office of Science and Technology Policy. Tahan is also Chief Scientist of the National Security Agency's Laboratory for Physical Sciences.
The superconducting tunnel junction (STJ) — also known as a superconductor–insulator–superconductor tunnel junction (SIS) — is an electronic device consisting of two superconductors separated by a very thin layer of insulating material. Current passes through the junction via the process of quantum tunneling. The STJ is a type of Josephson junction, though not all the properties of the STJ are described by the Josephson effect.
Circuit quantum electrodynamics provides a means of studying the fundamental interaction between light and matter. As in the field of cavity quantum electrodynamics, a single photon within a single mode cavity coherently couples to a quantum object (atom). In contrast to cavity QED, the photon is stored in a one-dimensional on-chip resonator and the quantum object is no natural atom but an artificial one. These artificial atoms usually are mesoscopic devices which exhibit an atom-like energy spectrum. The field of circuit QED is a prominent example for quantum information processing and a promising candidate for future quantum computation.
In quantum computing, and more specifically in superconducting quantum computing, a transmon is a type of superconducting charge qubit that was designed to have reduced sensitivity to charge noise. The transmon was developed by Robert J. Schoelkopf, Michel Devoret, Steven M. Girvin, and their colleagues at Yale University in 2007. Its name is an abbreviation of the term transmission line shunted plasma oscillation qubit; one which consists of a Cooper-pair box "where the two superconductors are also capacitatively shunted in order to decrease the sensitivity to charge noise, while maintaining a sufficient anharmonicity for selective qubit control".
Superconducting logic refers to a class of logic circuits or logic gates that use the unique properties of superconductors, including zero-resistance wires, ultrafast Josephson junction switches, and quantization of magnetic flux (fluxoid). Superconducting computing is a form of cryogenic computing, as superconductive electronic circuits require cooling to cryogenic temperatures for operation, typically below 10 kelvin. Often superconducting computing is applied to quantum computing, with an important application known as superconducting quantum computing.
Robert J. Schoelkopf III is an American physicist, most noted for his work on quantum computing as one of the inventors of superconducting qubits. Schoelkopf's main research areas are quantum transport, single-electron devices, and charge dynamics in nanostructures. His research utilizes quantum-effect and single-electron devices, both for fundamental physical studies and for applications. Techniques often include high-speed, high-sensitivity measurements performed on nanostructures at low temperatures. Schoelkopf serves as director of the Yale Center for Microelectronic Materials and Structures and as associate director of the Yale Institute for Nanoscience and Quantum Engineering. Since 2014, Schoelkopf is also the Director of the Yale Quantum Institute.
The DiVincenzo criteria are conditions necessary for constructing a quantum computer, conditions proposed in 2000 by the theoretical physicist David P. DiVincenzo, as being those necessary to construct such a computer—a computer first proposed by mathematician Yuri Manin, in 1980, and physicist Richard Feynman, in 1982—as a means to efficiently simulate quantum systems, such as in solving the quantum many-body problem.
Yasunobu Nakamura (中村 泰信 Nakamura Yasunobu) is a Japanese physicist. He is a professor at the University of Tokyo's Research Center for Advanced Science and Technology (RCAST) and the Principal Investigator of the Superconducting Quantum Electronics Research Group (SQERG) at the Center for Emergent Matter Science (CEMS) within RIKEN. He has contributed primarily to the area of quantum information science, particularly in superconducting quantum computing and hybrid quantum systems.
Irfan Siddiqi is an American physicist and currently a professor of physics at the University of California, Berkeley and a faculty scientist at Lawrence Berkeley National Laboratory (LBNL). He currently is the director of the Quantum Nanoelectronics Laboratory at UC Berkeley and the Advanced Quantum Testbed at LBNL. Siddiqi is known for groundbreaking contributions to the fields of superconducting quantum circuits, including dispersive single-shot readout of superconducting quantum bits, quantum feedback, observation of single quantum trajectories, and near-quantum limited microwave frequency amplification. In addition to other honors, for his pioneering work in superconducting devices, he was awarded with the American Physical Society George E. Valley, Jr. Prize in 2006, "for the development of the Josephson bifurcation amplifier for ultra-sensitive measurements at the quantum limit." Siddiqi is a fellow of the American Physical Society and a recipient of the UC Berkeley Distinguished Teaching Award in 2016.
Andreas Wallraff is a German physicist who conducts research in quantum information processing and quantum optics. He has taught as a professor at ETH Zürich in Zürich, Switzerland since 2006. He worked as a research scientist with Robert J. Schoelkopf at Yale University from 2002 to 2005, during which time he performed experiments in which the coherent interaction of a single photon with a single quantum electronic circuit was observed for the first time. His current work at ETH Zürich focuses on hybrid quantum systems combining superconducting electronic circuits with semiconductor quantum dots and individual Rydberg atoms as well as quantum error correction with superconducting qubits.
The ARC Centre of Excellence in Future Low-Energy Electronics Technologies is a collaboration of physicists, electrical engineers, chemists and material scientists from seven Australian universities developing ultra-low energy electronics aimed at reducing energy use in information technology (IT). The Centre was funded in the 2017 ARC funding round.
Xiaolin Wang is a Chinese-Australian scientist recognised for his work in advanced materials synthesis and characterisation and spintronics. He is director of the Institute for Superconducting and Electronic Materials, University of Wollongong. Wang is a University of Wollongong senior professor, and an Australian Research Council future fellow.
John M. Martinis is an American physicist and a professor of physics at the University of California, Santa Barbara. In 2014, the Google Quantum A.I. Lab announced that it had hired Martinis and his team to build a quantum computer using superconducting qubit.
