Abstract: A finger SQUID qubit device and method for performing quantum computation with said device is disclosed. A finger SQUID qubit device includes a superconducting loop and one or more superconducting fingers, wherein the fingers extend to the interior of said loop. Each finger has a mesoscopic island at the tip, separated from the rest of the finger by a Josephson junction. A system for performing quantum computation with the finger SQUID qubit device includes a mechanism for initializing, entangling, and reading out the qubits. The mechanism may involve passing a bias current across the leads of the superconducting loop and a mechanism for measuring a potential change across the leads of the superconducting loop. Furthermore, a control system includes a mechanism for addressing specific qubits in a quantum register of finger SQUID devices.

Abstract: A finger SQUID qubit device and method for performing quantum computation with said device is disclosed. A finger SQUID qubit device includes a superconducting loop and one or more superconducting fingers, wherein the fingers extend to the interior of said loop. Each finger has a mesoscopic island at the tip, separated from the rest of the finger by a Josephson junction. A system for performing quantum computation with the finger SQUID qubit device includes a mechanism for initializing, entangling, and reading out the qubits. The mechanism may involve passing a bias current across the leads of the superconducting loop and a mechanism for measuring a potential change across the leads of the superconducting loop. Furthermore, a control system includes a mechanism for addressing specific qubits in a quantum register of finger SQUID devices.

Abstract: A control system for an array of qubits is disclosed. The control system according to the present invention provides currents and voltages to qubits in the array of qubits in order to perform functions on the qubit. The functions that the control system can perform include read out, initialization, and entanglement. The state of a qubit can be determined by grounding the qubit, applying a current across the qubit, measuring the resulting potential drop across the qubit, and interpreting the potential drop as a state of the qubit. A qubit can be initialized by grounding the qubit and applying a current across the qubit in a selected direction for a time sufficient that the quantum state of the qubit can relax into the selected state. In some embodiments, the qubit can be initialized by grounding the qubit and applying a current across the qubit in a selected direction and then ramping the current to zero in order that the state of the qubit relaxes into the selected state.

Abstract: A finger SQUID qubit device and method for performing quantum computation with said device is disclosed. A finger SQUID qubit device includes a superconducting loop and one or more superconducting fingers, wherein the fingers extend to the interior of said loop. Each finger has a mesoscopic island at the tip, separated from the rest of the finger by a Josephson junction. A system for performing quantum computation with the finger SQUID qubit device includes a mechanism for initializing, entangling, and reading out the qubits. The mechanism may involve passing a bias current across the leads of the superconducting loop and a mechanism for measuring a potential change across the leads of the superconducting loop. Furthermore, a control system includes a mechanism for addressing specific qubits in a quantum register of finger SQUID devices.

Abstract: The present invention comprises a junction between an unconventional superconductor, an intermediate material, and a conventional superconducting material. In some embodiments, the unconventional superconductor has an orthorhombic crystal structure and the supercurrent in the resulting junction flows in the c-axis direction of the orthorhombic crystal. In other embodiments, the supercurrent flows parallel to a direction in the a-b plane. Interface junctions according to embodiments of the present invention may be used in superconducting low inductance qubits (SLIQs) and in permanent readout superconducting qubits (PRSQs), can form the basis of quantum registers, and can permit parity keys or other devices made from conventional superconducting material to be attached to qubits made from unconventional superconducting material or vice versa.

Abstract: A method for inserting fluxons into an annular Josephson junction is disclosed. Fluxon injection according to the present invention is based on local current injection into one of the superconducting electrodes of the junction. By choosing an appropriate value for the injection current, which depends upon the spacing between injecting leads among other factors, the residual fluxon pinning can be reduced to a very small level. Fluxon injection according to the present invention provides for fully controlling the trapping of individual fluxons in annular Josephson junctions and is reversible to a state of zero fluxons without heating the Josephson above its critical temperature. Fluxon injection according to the present invention can be used for preparing the working state of fluxon oscillators, clock references, radiation detectors and shaped junctions that may be used as qubits for quantum computing.