Form and fabrication of semiconductor-superconductor nanowires and quantum devices based thereon
The disclosure relates to a quantum device and method of fabricating the same. The device comprises one or more semiconductor-superconductor nanowires, each comprising a length of semiconductor material and a coating of superconductor material coated on the semiconductor material. The nanowires may be formed over a substrate. In a first aspect at least some of the nanowires are full-shell nanowires with superconductor material being coated around a full perimeter of the semiconductor material along some or all of the length of the wire, wherein the device is operable to induce at least one Majorana zero mode, MZM, in one or more active ones of the full-shell nanowires. In a second aspect at least some of the nanowires are arranged vertically relative to the plane of the substrate in the finished device.
1. A device comprising one or more semiconductor-superconductor nanowires, each comprising a length of semiconductor material and a coating of superconductor material coated on the semiconductor material;
wherein each of one, some or all of the nanowires is a full-shell nanowire, the superconductor material being coated around a full perimeter of the semiconductor material along some or all of the length of the semiconductor material; and
wherein the device is operable to induce at least one Majorana zero mode, MZM, in one or more active ones of the nanowires including at least one or more of the full-shell nanowires by application of a magnetic field component parallel to the active nanowires.
2. The device of claim 1 , wherein the device is operable to induce the MZMs at least by application of the magnetic field component from outside the device.
3. The device of claim 1 , wherein the device comprises a substrate and one or more layers formed over the substrate, wherein the nanowires are formed in one or more of said layers.
4. The device of claim 3 , wherein one, some or all of the full-shell nanowires are vertical relative to the substrate.
5. The device of claim 4 , further comprising at least one layer of filler material disposed between the vertical nanowires to mechanically support the vertical nanowires.
6. The device of claim 3 , wherein one, some or all of the full-shell nanowires are horizontal in the plane of the substrate.
7. The device of claim 3 , further comprising one or more layers of circuitry formed in one or more of said layers, for connecting the nanowires together into quantum structures, controlling the nanowires or quantum structures, and/or taking measurements from the nanowires or quantum structures.
8. The device of claim 7 , wherein one or more of the nanowires other than active nanowires are arranged as conductive vias between layers of the circuitry or a layer of the circuitry an exterior of the device.
9. The device of claim 7 , wherein the one or more layers of circuitry comprise a semiconducting network that connects the active nanowires, for opening or closing tunnel junctions in the semiconducting network.
10. The device of claim 1 , wherein the device comprises one or more qubits, each qubit comprising a plurality of the active nanowires, wherein one, some or all of the plurality of nanowires in each qubit are full-shell nanowires.
11. The device of claim 10 , wherein each of the qubits is either: a tetron qubit in which said plurality is four, or hexon qubit in which said plurality is six.
12. The device of claim 4 , wherein:
the device comprises one or more qubits, each qubit comprising a plurality of the active nanowires, wherein one, some or all of the plurality of nanowires in each qubit are full-shell nanowires; and
each qubit comprises a horizontal superconducting island formed in a plane paralleled to the substrate, wherein the superconducting island is divided into arms each joining the lower end of a respective one of the plurality of vertical nanowires in the qubit to a common point of the superconducting island.
13. The device of claim 12 , wherein the arms take the form of concentric spiral arms.
14. The device of claim 12 , wherein the superconducting island of each qubit is formed of the same superconductor material as the coating of the nanowires.
15. The device of claim 1 , wherein the device is packaged in an integrated circuit package.
16. The device of any preceding claim, wherein one or more of:
the semiconductor material is InAS or InSb,
the superconductor material is Al or Nb, and/or
the filler material comprises a plastic or wax.
17. A quantum computer comprising:
the device of claim 1 ; and
an electromagnet arranged to apply the magnetic field component parallel to the active nanowires.
18. The quantum computer of claim 17 , comprising a refrigerated chamber in which the device is placed in order to induce superconductivity in the superconductor.
19. A method of operating the device of any of claim 1 , the method comprising:
applying the magnetic field component parallel to the active nanowires in order to induce the at least one MZM in each of the active nanowires;
wherein said inducement comprises a winding of a superconducting phase of the superconductor material, introduced by a magnetic flux of the magnetic field component through the active nanowires, coupling to the magnetic field component in order to induce a topological phase by means of an orbital effect of the magnetic field component.
20. The method of claim 19 , comprising refrigerating the device to induce superconductivity in the superconductor material.