Noise-bias preserving gate with qubits encoded in an superconducting Ising chain

Building qubits with intrinsic protection against noise is a promising approach to realize a useful quantum computer. It is possible to encode protected quantum information in Majorana zero modes found in the Kitaev model, but their implementation remains experimentally challenging. Alternatively, a qubit can be encoded in the degenerate ground states of the transverse field Ising model, the spin counterpart of the Kitaev model. Similar to cat qubits [1], the Ising chain qubit is noise-biased; it is immune to bit flips but sensitive to phase flips. This property can be used to implement more efficient error correcting codes [2].

In this work, we show that a noise-bias preserving X gate can be performed on an Ising chain implemented using superconducting qubits. The gate is realized by sequentially and adiabatically turning off and on the coupling between the individual qubits forming the chain. The operation can be faster than 50 ns for realistic system parameters, does not require any RF signal, and is robust to large deviations in control parameters, up to 50 %. Our theoretical results show that the Ising chain qubit is a promising architecture to protect quantum information encoded in a superconducting platform.

[1] Grimm et al., Nature 584 205 (2020)

[2] Aliferis et al., PRA 78, 052331 (2008)