Fluxon injection into annular josephson junctions

Abstract

A method and apparatus 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.

I claim:  
     
         1 . A fluxon injection system comprising: 
 an annular Josephson junction; and    current injection electrodes electrically connected to a superconducting electrode of the annular Josephson junction to form the flux injection system.    
     
     
         2 . The system of  claim 1 , wherein the annular Josephson junction is a long Josephson junction.  
     
     
         3 . The system of  claim 1 , wherein the annular Josephson junction is substantially circular in shape.  
     
     
         4 . The system of  claim 1 , wherein the annular Josephson junction is heart-shaped.  
     
     
         5 . The system of  claim 1 , wherein the annular Josephson junction has a Lyngby geometry.  
     
     
         6 . The system of  claim 1 , wherein the annular Josephson junction forms a qubit.  
     
     
         7 . The system of  claim 1 , wherein the annular Josephson junction comprises Nb/Al—AlO x /Nb.  
     
     
         8 . The system of  claim 7 , wherein the annular Josephson junction has a mean diameter of approximately 100 μm and a junction width of approximately 4 μm.  
     
     
         9 . The system of  claim 8 , wherein spacing between the injection electrodes is in a range from approximately 10 μm to approximately 22μ.  
     
     
         10 . The system of  claim 1 , wherein spacing between the current injection electrodes is between approximately a value of the Josephson penetration depth to approximately a width of the current injection leads.  
     
     
         11 . A method of injecting at least one fluxon into an annular Josephson junction comprising: 
 providing current carrying injection electrodes electrically connected to a superconducting electrode of the annular Josephson junction; and,    delivering an injection current through the injection electrodes wherein the injection current has sufficient magnitude that the magnetic flux generated in the junction of the Josephson junction by the passage of the injection current therethrough is sufficient to create at least one fluxon in the Josephson junction.    
     
     
         12 . The method of  claim 11 , wherein the magnetic flux generated by the injection current is at least twice the quantum of magnetic flux.  
     
     
         13 . The method of  claim 11 , wherein the annular Josephson junction is a long Josephson junction.  
     
     
         14 . The method of  claim 11 , wherein the annular Josephson junction is substantially circular in shape.  
     
     
         15 . The method of  claim 11 , wherein the annular Josephson junction is heart-shaped.  
     
     
         16 . The method of  claim 11 , wherein the annular Josephson junction has a Lyngby geometry.  
     
     
         17 . The method of  claim 11 , wherein the annular Josephson junction comprises Nb/Al—AlO x /Nb.  
     
     
         18 . The method of  claim 17 , wherein the annular Josephson junction has a mean diameter of approximately 100 μm and a junction width of approximately 4 μm.  
     
     
         19 . The method of  claim 18 , wherein a spacing between the injection electrodes is in a range from approximately 10 μm to approximately 22 μm.  
     
     
         20 . The method of  claim 19 , wherein the injection current is between approximately 3 mA to approximately 10 mA.  
     
     
         21 . A fluxon as an article of manufacture wherein the fluxon is produced according to the process of  claim 11 .  
     
     
         22 . A plurality of fluxons produced according to the process of  claim 11 .  
     
     
         23 . The method of  claim 11 , wherein a spacing between the injection electrodes is in a range from approximately a value of the Josephson penetration depth to approximately a width of the current injection leads.  
     
     
         24  The method of  claim 11 , wherein the annular Josephson junction forms a qubit.  
     
     
         25 . A method of creating and destroying fluxons in a Josephson junction comprising: 
 providing current carrying injection electrodes electrically connected to a superconducting electrode of the Josephson junction; and,    delivering an injection current through the injection electrodes wherein the injection current has sufficient magnitude that the magnetic flux generated in the junction of the Josephson junction by the passage of the injection current therethrough is sufficient to create at least one fluxon in the Josephson junction; and    reducing the injection current to zero thereby returning the Josephson junction to a state without fluxons.    
     
     
         26 . The method of  claim 25 , wherein the magnetic flux generated by the injection current is at least twice the quantum of magnetic flux.  
     
     
         27 . The method of  claim 25 , wherein the annular Josephson junction is a long Josephson junction.  
     
     
         28 . The method of  claim 25 , wherein the annular Josephson junction is substantially circular in shape.  
     
     
         29 . The method of  claim 25 , wherein the annular Josephson junction is heart-shaped.  
     
     
         30 . The method of  claim 25 , wherein the annular Josephson junction has a Lyngby geometry.  
     
     
         31 . The method of  claim 25 , wherein spacing between the injection electrodes is in a range from approximately a value of the Josephson penetration depth to approximately a width of the current injection leads.  
     
     
         32 . The method of  claim 25 , wherein the annular Josephson junction forms a qubit.