Guo-Liang Guo

Parity-protected superconducting qubit based on topological insulators

  1. Guo-Liang Guo,
  2. Han-Bing Leng,
  3. and Xin Liu
We propose a novel architecture that utilizes two 0-π qubits based on topological Josephson junctions to implement a parity-protected superconducting qubit. The topological Josephson
junctions provides protection against fabrication variations, which ensures the identical Josephson junctions required to implement the0-π qubit. By viewing the even and odd parity ground states of a 0-π qubit as spin-12 states, we construct the logic qubit states using the total parity odd subspace of two 0-π qubits. This parity-protected qubit exhibits robustness against charge noise, similar to a singlet-triplet qubit’s immunity to global magnetic field fluctuations. Meanwhile, the flux noise cannot directly couple two states with the same total parity and therefore is greatly suppressed. Benefiting from the simultaneous protection from both charge and flux noise, we demonstrate a dramatic enhancement of both T1 and T2 coherence times. Our work presents a new approach to engineer symmetry-protected superconducting qubits.
arxiv pdf

0-π qubit in one Josephson junction

  1. Guo-Liang Guo,
  2. Han-Bing Leng,
  3. Yong Hu,
  4. and Xin Liu
Quantum states are usually fragile which makes quantum computation being not as stable as classical computation. Quantum correction codes can protect quantum states but need a large
number of physical qubits to code a single logic qubit. Alternatively, the protection at the hardware level has been recently developed to maintain the coherence of the quantum information by using symmetries. However, it generally has to pay the expense of increasing the complexity of the quantum devices. In this work, we show that the protection at the hardware level can be approached without increasing the complexity of the devices. The interplay between the spin-orbit coupling and the Zeeman splitting in the semiconductor allows us to tune the Josephson coupling in terms of the spin degree of freedom of Cooper pairs, the hallmark of the superconducting spintronics. This leads to the implementation of the parity-protected 0-π superconducting qubit with only one highly transparent superconductor-semiconductor Josephson junction, which makes our proposal immune from the various fabrication imperfections.
arxiv pdf