Superinductance for hardware-protected superconducting qubits
The quantum computer dream is driven by promises of unprecedented capabilities but is also facing a stark reality: quantum coherence is as powerful as it is difficult to protect. Quantum Error Correction (QEC) aims to extend coherence using redundancies but leads to solutions that are extremely resource-intensive: at present, protecting one bit of information requires at least ten thousand physical qubits. The main objective of this proposal is to engineer a new type of superconducting qubit, which will be intrinsically protected against de-coherence. Instead of matching the qubit states to the number of Cooper pairs or flux quanta of a given circuit, as is usually done, SuperProtected will exploit a completely new encoding scheme: quantum information will be stored as the parity of the number of Cooper pairs. This will be achieved by building a circuit component where charge transport occurs as pairs of Cooper pairs (4e-tunneling) while the standard single pair transport (2e-tunneling), or Josephson current, is reduced to zero. This new paradigm implies inductances with unprecedented value (10μH), also known as superinductances. The novel approach builds on two technological steps: a new high-kinetic inductance superconductor (InOx) and suspended silicon membranes. Improvement of the coherence time over current state-of-the-art is expected to be two orders of magnitude. The proposed qubits offer another major advantage: protected gates can be implemented using a simple modification of the architecture. The resulting protected qubit will extend the frontiers of the current knowledge in QEC and bring down the hardware requirements for a logical qubit by several orders of magnitude. Such a result would considerably change the quantum computing landscape.