GERSHENSON LAB

Quantum Computing with Nanoscale Josephson Junctions

We have developed two novel Josephson circuits intended as prototypes of protected qubits whose logical states are decoupled from the environment by encoding them in a parity of a large number. The first type, the so-called charge-pairing qubit [1], represents a chain of two Josephson elements characterized by the π periodicity of the phase dependence of their Josephson energy (the so-called Josephson rhombi [2]). The second type, the flux-pairing qubit [3], consists of a 4π periodic Josephson element (a Cooper pair box with the e charge on the central island) shunted by a superinductor [4]. The lowest-energy quantum states of the charge-pairing qubit are encoded in the parity of Cooper pairs on a superconducting island flanked by the Josephson rhombi. The flux-pairing qubit encodes its quantum states in the parity of magnetic flux quanta inside a superconducting loop.

1. M.T. Bell, J. Paramanandam, L.B. Ioffe, and M.E. Gershenson. Protected Josephson Rhombus Chains. Phys. Rev. Lett. 112, 167001 1-5 (2014).

2. S. Gladchenko, D. Olaya, E. Dupont-Ferrier, B. Doucot, L.B. Ioffe, and M.E. Gershenson. Superconducting Nanocircuits for Topologically Protected Qubits. Nature Physics 5, 48-53 (2009).

3. M.T. Bell, W. Zhang, L. B. Ioffe, and M. E. Gershenson. Spectroscopic Evidence of the Aharonov-Casher Effect in a Cooper Pair Box. Phys. Rev. Lett. 116, 107002 (2016).

4. M.T. Bell, I.A. Sadovskyy, L.B. Ioffe, A.Yu. Kitaev, and M.E. Gershenson. Quantum Superinductor with Tunable Non-Linearity. Phys. Rev. Lett. 109, 137003 (2012).