One of the significant challenges in developing a scalable quantum information processor with electron spins is the achievement of a long-range spin-spin interaction. Our approach is to interface spin qubits with photons in the circuit quantum electrodynamics (cQED) architecture . In cQED, the qubits are coupled to a superconducting transmission line resonator, which acts as a 'cavity'. Strong qubit-cavity interactions can allow for long-range qubit-qubit interactions, with the cavity acting as a 'quantum bus'. cQED has been used to successfully couple multiple superconducting qubits over relatively large distances (several millimeters) .
We have recently demonstrated the integration of a spin qubit into the cQED architecture. The hybridization of spin and superconducting technologies presents some challenges, since superconductors perform poorly in magnetic fields. Magnetic fields are required to Zeeman split the spin states. The spin qubit, formed in an InAs nanowire double quantum dot device (b), is placed at one of the anti-nodes of a half-wavelength niobium thin-film resonator (a). To effectively couple the spin qubit to the electric field of the cavity we take advantage of the strong spin-orbit interaction in InAs which couples the motional and spin degrees of freedom (c). We find that the transmission through the cavity is extremely sensitive to the position of an electron in the nanowire double quantum dot (d-e). By applying single spin rotations and utilizing the Pauli exclusion principle for spin-to-charge conversion we are able to perform single spin readout using the superconducting cavity (f).
Future work includes using the cQED architecture to further explore coherence in InAs nanowires and other ultra-coherent materials such as Ge/Si core/shell nanowires. We are also interested in using our hybrid system to characterize photon emission from the cavity in the regime where current is driven through the double quantum dot device.
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