Microwave circulator
A microwave circulator including an integrated circuit and having a number of ports, a respective superconducting ring segment coupled to each port to allow microwave frequency signals to be transferred between the port and the respective ring segment, a superconducting tunnel junction interconnecting each pair of adjacent ring segments to form a circulator ring, wherein the tunnel junctions are configured so that when a bias is applied to the tunnel junctions, signals undergo a phase shift as they traverse the tunnel junctions between ring segments, thereby propagating signals to an adjacent port in a propagation direction and at least one feature to at least partially suppress quasiparticles within the circulator.
1 . A microwave circulator including an integrated circuit and having:
a) a number of ports;
b) a respective superconducting ring segment coupled to each port to allow microwave frequency signals to be transferred between the port and the respective ring segment;
c) a superconducting tunnel junction interconnecting each pair of adjacent ring segments to form a circulator ring, wherein the tunnel junctions are configured so that when a bias is applied to the tunnel junctions, signals undergo a phase shift as they traverse the tunnel junctions between ring segments, thereby propagating signals to an adjacent port in a propagation direction; and,
d) at least one feature to at least partially suppress quasiparticles within the circulator, wherein the at least one feature includes trap superconducting material deposited on each of the ring segments.
2 . A microwave circulator according to claim 1 , wherein the at least one feature includes gap engineering of one or more of the tunnel junctions.
3 . A microwave circulator according to claim 2 , wherein each tunnel junction includes superconducting electrodes separated by a tunnelling barrier, and wherein at least one of:
a) the electrodes have different thicknesses; and,
b) the electrodes are made of different superconducting materials.
4 . A microwave circulator according to claim 1 , wherein at least one of:
a) the propagation direction is dependent on at least one of a magnitude and polarity of the bias;
b) propagation is controlled by adjusting at least one of a magnitude and polarity of the bias; and,
c) propagation is controlled so that circulator acts as at least one of:
i) a switch;
ii) an isolator;
iii) a duplexer;
iv) a filter; and,
v) an attenuator.
5 . A microwave circulator according to claim 1 , wherein the bias includes:
a) a central bias applied to all of the tunnel junctions; and,
b) a segment bias applied to tunnel junctions between each ring segment.
6 . A microwave circulator according to claim 5 , wherein the bias includes:
a) the central bias generated by applying a magnetic field to the ring; and,
b) the segment bias generated by applying a bias voltage to each ring segment.
7 . A microwave circulator according to claim 1 , wherein each port is capacitively coupled to a respective ring segment.
8 . A microwave circulator according to claim 1 , wherein the tunnel junctions are Josephson junctions.
9 . A microwave circulator according to claim 1 , wherein the integrated circuit includes:
a) a substrate;
b) a first superconducting material deposited on the substrate that is to form a lower electrode of each junction;
c) an insulating layer provided on at least part of a first conductive material that forms tunnelling barrier of the junctions; and,
d) a second superconducting material deposited on the insulating layer and spanning adjacent lower electrodes to form counter electrodes of each junction.
10 . A microwave circulator according to claim 9 , wherein at least one of:
a) the first and second superconducting materials are made of at least one of:
i) niobium; and,
ii) aluminium; and,
b) the insulating layer is made of aluminium oxide.
11 . A microwave circulator according to claim 1 , wherein the circulator includes at least three of the ports and three of the ring segments.