Supercurrent devices

Claim 2

A supercurrent device comprising: a pair of superconductive regions; a weak-link interfacial region joining said superconductive regions; said device having a hysteretic current voltage characteristic including a region of increasing current aT zero voltage and first critical current at which the interfacial voltage abruptly increases from the zero voltage to some finite higher value; and including a region of decreasing current less than the first critical current in which the interfacial voltage decreases and a second critical current, less than the first critical current, at which the interfacial voltage is again zero, said second critical current being nearly zero and varying in magnitude as a function of noise; means for applying to said interfacial region current, the amplitude of which is variable from greater than the first critical current to less than the second critical current; and means for establishing an increased fixed value of said second critical current comprising an electrically conductive member connected in shunt across said interfacial region.

Claim 3

The device of claim 1 wherein said interfacial region comprises an insulative member separating said superconductive regions and contiguous with at least a portion of each of said superconductive regions.

Claim 4

The device of claim 2 wherein said superconductive regions and said insulative member are planar thin films.

Claim 5

The device of claim 3 wherein said conductive member comprises a normal metal thin film in electrical contact with each of said superconductive regions.

Claim 6

The device of claim 4 wherein said conductive member is characterized by an inductance proportional to the amount of magnetic flux coupling said normal metal member and in combination with a superconducting ground plane, an insulative layer deposited on said ground plane, said device being fabricated on said insulative layer to reduce the magnitude of the inductance of said conductive member by reducing the flux coupling said normal metal member.

Claim 7

The device of claim 2 wherein one of said superconductive regions has a tapered region defining a small cross-sectional area in the vicinity of said interfacial region, and said insulative member is contiguous with the small cross-sectional area of said superconductive region.

Claim 8

The device of claim 6 wherein said tapered region of said one superconductive region is one-dimensional defining a wedge.

Claim 9

The device of claim 6 wherein said tapered region of said one superconductive region is two-dimensional defining a point.

Claim 10

The device of claim 6 wherein said conductive member comprises a normal metal thin film deposited on at least a portion of the surface of said insulative member, said metal film having an aperture exposing a portion of the surface of said insulative member, said tapered region of said other superconductive region making electrical contact with said insulative member and with the side of the aperture.

Claim 11

The device of claim 9 wherein the lateral distance d between the point of contact of said tapered region with said insulative member and the point of contact with the side of the aperture is such that where lambda is the wavelength of Josephson oscillations, h is Planck''s constant, c is the velocity of light, G is the magnitude of the conductance of said conductive member e is the electronic charge and iJ is the Josephson supercurrent.

Claim 12

The device of claim 1 wherein one of said superconductive regions has a tapered region defining a small cross-sectional area in body-to-body contact with said other superconductive region, and said interfacial region comprises the region of contact of said superconductive regions.

Claim 13

The device of claim 11 wherein said tapered region is one-dimensional defining a wedge.

Claim 14

The device of claim 11 wherein said tapered region is two-dimensional defining a point.

Claim 15

The device of claim 11 wherein said conductive member comprises a normal metal thin film deposited on at least a portion of the surface of said other superconductive region, said metal film having an aperture exposing a portion of the surface of said other superconductive region, said tapEred region of said one superconductive region making electrical contact with said other superconductive region and the side of the aperture.

Claim 16

The device of claim 14 wherein the distance d between the point of contact of said tapered region with the exposed region of said other superconductor and the point of contact with the side of the aperture is such that where lambda is the wavelength of Josephson oscillations h is Planck''s constant, c is the velocity of light, G is the magnitude of the conductance of said conductive member, e is the electronic charge and iJ is the Josephson super current.

Claim 17

The device of claim 1 comprising an elongated superconductive member having a tapered region intermediate the ends thereof defining said pair of superconductive regions on either side of said tapered region and further defining said interfacial region as the region of minimum cross section of said tapered region of minimum cross section of said tapered region and an insulative region electrically separating said conductive member from said interfacial region.

Claim 18

The device of claim 16 wherein said conductive member comprises a normal metal member in electrical contact with each of said superconductive regions.

Claim 19

The device of claim 17 wherein said conductive member is characterized by an inductance proportional to the amount of magnetic flux coupling said normal metal member and in combination with a superconducting ground plane, an insulative layer deposited on said ground plane, said device being fabricated in planar thin film form on said insulative layer to reduce the magnitude of the inductance of said conductive member by reducing the flux coupling said normal metal member.

Claim 20

A supercurrent device comprising: a pair of superconductive regions; a weak-link interfacial region joining said superconductive regions; said device having a hysteretic current voltage characteristic including a region of increasing current at zero voltage and a first critical current at which the interfacial voltage abruptly increases from the zero voltage to some finite higher value; and including a region of decreasing current less than the first critical current in which the interfacial voltage decreases and a second critical current, less than the first critical current, at which the interfacial voltage is again zero, said second critical current being nearly zero and varying in magnitude as a function of noise; means for establishing an increased value of said second critical current comprising an electrically conductive member connected in shunt across said interfacial region; means for applying a fixed bias current to said interfacial region; and means for applying to said interfacial region a variable magnetic field such that an increase in the magnitude field reduces the first critical current below the fixed bias current thereby to increase the voltage of said interfacial region from zero voltage toe finite higher value, and such that a decrease in the magnitude of the field increase the second critical current above the fixed bias value thereby to decrease the voltage of said interfacial region to zero voltage again.

Claim 21

A supercurrent device comprising: a pair of superconductive regions; a weak-link interfacial region joining said superconductive regions; said device having a hysteretic current voltage characteristic including a region of increasing current at zero voltage and a first critical current at which the interfacial voltage abruptly increases from the zero voltage to some finite higher value; and including a region of decreasing current less than the first critical current in which the interfacial voltage decreases and a second critical current, less than the first critical current, at which the interfacial voltage is again zero, said second critical current being nearly zero and varying in magnitude as a function of noise; means for establishing an increased value of said second critical current comprising an electrically conductive member connected in shunt across said interfacial region; means for applying a fixed bias current to said interfacial region; and means for applying to said interfacial region a variable magnetic field such that an increase in the magnitude field reduces the first critical current below the fixed bias current thereby to increase the voltage of said interfacial region from zero voltage toe finite higher value, and such that a decrease in the magnitude of the field increase the second critical current above the fixed bias value thereby to decrease the voltage of said interfacial region to zero voltage again.