We describe the fabrication and measurement of a micrometer-sized direct-current superconducting quantum interference device ͑dc-SQUID͒ in which the critical currents of each of the constriction-type Josephson junctions can be controlled independently and in situ via a process of nonequilibrium ͑hot-phonon͒ irradiation from a nanofabricated gated structure. The control mechanism is based on hot phonons which are injected into the superconducting microbridges from close proximity, but electrically isolated, normal-metal constrictions. We have also developed a one-dimensional computer model to analyze the behavior of micro-SQUID devices including situations in which we modify the asymmetry of the device. We show from the model that the experimental results are consistent with a change in effective length of the microbridge junctions with respect to the coherence length of the film. The experimental data, and its interpretation in relation to the micro-SQUID model, confirm that this technique, based on hot-phonon irradiation for controlling the critical current in Dayem bridge Josephson junctions, is compatible with the Josephson effect and a feasible method for post-fabrication parameter control in superconducting circuits using Dayem bridge Josephson junctions.

We show how the measurement induced model of quantum computation proposed by Raussendorf and Briegel [Phys. Rev. Letts. 86, 5188 (2001)] can be adapted to a nonlinear optical interaction. This optical implementation requires a Kerr nonlinearity, a single photon source, a single photon detector and fast feed forward. Although nondeterministic optical quantum information proposals such as that suggested by KLM [Nature 409, 46 (2001)] do not require a Kerr nonlinearity they do require complex reconfigurable optical networks. The proposal in this paper has the benefit of a single static optical layout with fixed device parameters, where the algorithm is defined by the final measurement procedure.Comment: 14 pages, 4 figures, 4 table

The direct current superconducting quantum interference device (DC-SQUID), using controlled Josephson junction technology, provides a mechanism to modify the characteristics of the device post-fabrication. We report on the fabrication and measurement of a micron sized DC-SQUID using two Dayem bridge weak-link Josephson junctions with integrated “heaters.” The weak link critical current is controlled by hot phonons from the current biased titanium, normal metal heater. By using the heaters, control over the critical current oscillations of the SQUID was observed at 4.2K.

We describe the fabrication and digital logic operation of superconducting nanotransistors. The nanotransistor is a superconducting weak-link device that has integrated hot-phonon injector heaters to control its switching critical current. The fabrication process utilizes a self-aligned method, where the heater acts as a mask for reactive ion etching to define the device pattern. This device is much simpler to fabricate than previously reported controllable superconducting transistors and the principle of operation makes it possible to use a single nanotransistor connected to a load resistor as a NOT logic gate, allowing lower power consumption and improved levels of integration.

We show how the measurement induced model of quantum computation proposed by Raussendorf and Briegel [Phys. Rev. Letts. 86, 5188 (2001)] can be adapted to a nonlinear optical interaction. This optical implementation requires a Kerr nonlinearity, a single photon source, a single photon detector and fast feed forward. Although nondeterministic optical quantum information proposals such as that suggested by KLM [Nature 409, 46 (2001)] do not require a Kerr nonlinearity they do require complex reconfigurable optical networks. The proposal in this paper has the benefit of a single static optical layout with fixed device parameters, where the algorithm is defined by the final measurement procedure.