Symmetry Protected Qubits Through Fluxon Pairing*

We present time-domain experiments with symmetry-protected qubits whose quantum states are encoded in the parity of fluxons in a superconducting loop. The qubit is composed of a Cooper pair box and a superinductor arranged in a superconducting loop [1]. The lowest-energy states of this qubit correspond to even/odd parity of fluxons in the loop. We will discuss proof-of-concept experiments that show how the qubit can be placed into a state protected against energy relaxation where the fluxon parity is preserved through the Aharonov-Casher interference. We will show that using fast gate pulses, the fluxon-pairing qubit can by adiabatically switched between the protected and unprotected states for quantum state initialization and readout. We will also discuss preliminary results on the implementation of fluxon-pairing qubits with superinductors fabricated from meandered nanowires made of strongly disordered Aluminum [2].
[1]. M.T. Bell, W. Zhang et.al. Phys. Rev. Lett. 116, 107002 (2016).
[2]. W. Zhang, K. Kalashnikov et. al. arXiv:1807.00210 (2018).