Ziqi Xu

I write research software for quantum many-body physics: neural quantum states, tensor networks and exact diagonalization, mostly in Python with PyTorch, NetKet, JAX and TeNPy.

I completed my M.Sc. in Physics at the University of Waterloo in 2026, supervised by Robert Mann and Tim Hsieh, as an associate graduate student at the Perimeter Institute. My thesis research looks at the classical correlations that measurement creates in 1D cluster states, quantified by conditional mutual information, and what they mean for how well neural networks can represent these states. Before Waterloo I studied theoretical physics at Nankai University.

I’m looking for quantum software engineering roles in Canada. You can reach me at z559xu@uwaterloo.ca, and my CV is here.

Projects

• Neural quantum states and exact MPS diagnostics

  RBM and RNN variational ansätze for 1D spin chains, and exact transfer-matrix code for the conditional mutual information of the measured cluster state, tested against brute-force state vectors.

  Python · NetKet · PyTorch · TeNPy · pytest · GitHub Actions

• Lane–Emden polytropes

  A stellar-structure ODE solver checked against analytic solutions, with a phase-space analysis of the special case n = 5. It revisits my undergraduate research with Prof. Yu-Qing Lou.

  Python · SciPy · unittest · GitHub Actions

• Entangled sensor arrays under phase disorder

  Quantum Fisher information of GHZ and product probes computed with squint (JAX): random signal phases erase the Heisenberg advantage, and X gates on the right sensors recover 0.41 N².

  Python · JAX · squint · NumPy · pytest · GitHub Actions

Writing

• Expressive is not the same as learnableSep 2026

  A rotated cluster state is an exact bond-dimension-2 matrix product state, so the complex variational models I trained never lacked the capacity to represent it. How easily each one learned it tracked whether its hidden update had the shape of that two-dimensional memory.

• What phase disorder does to the GHZ advantageSep 2026

  With squint, a JAX library for differentiable quantum metrology, the quantum Fisher information of a GHZ sensor array under random signal phases takes a few lines. The Heisenberg advantage disappears, and a handful of X gates brings most of it back.

• How far do measurement correlations reach in a cluster state?Sep 2026

  Measuring a 1D cluster state in a tilted basis correlates distant outcomes. An exact matrix-product-state calculation shows how far those correlations reach.