Shashank Soyuz Virmani

arXiv2023

The two-qubit singlet/triplet measurement is universal for quantum computing given only maximally-mixed initial states

We prove the STP=BQP conjecture of Freedman, Hastings and Shokrian-Zini [1], namely that the two-qubit singlet/triplet measurement is quantum computationally universal given only an initial ensemble of maximally mixed single qubits. This provides a method for quantum computing that is fully rotationally symmetric (i.e. reference frame independent), using primitives that are both physically very-accessible and provably the simplest possible.

quant-ph↗

arXiv2005

A relational quantum computer using only two-qubit total spin measurement and an initial supply of highly mixed single qubit states

We prove that universal quantum computation is possible using only (i) the physically natural measurement on two qubits which distinguishes the singlet from the triplet subspace, and (ii) qubits prepared in almost any three different (potentially highly mixed) states. In some sense this measurement is a `more universal' dynamical element than a universal 2-qubit unitary gate, since the latter must be supplemented by measurement. Because of the rotational invariance of the measurement used, our scheme is robust to collective decoherence in a manner very different to previous proposals - in effect it is only ever sensitive to the relational properties of the qubits.

quant-ph↗