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Glossary

Quantum glossary

Measurement-induced phase transition

Also: MIPT, entanglement transition, hybrid circuit

A sharp change in how entangled a quantum circuit’s state is, as the rate of mid-circuit measurements crosses a critical value.

Random gates build entanglement and measurements remove it. Below the critical measurement rate entanglement grows with system size; above it, it does not. The transition is invisible in the average state — it shows up only when each run is examined together with its own measurement record, which is what makes it hard to observe on hardware.

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Related terms

  • Entanglement entropy — A number, in bits, for how entangled one part of a pure quantum state is with the rest.
  • Measurement — Reading out a qubit, which returns a classical bit sampled by the Born rule and leaves the qubit in the state matching it.
  • Clifford gates — The gates — generated by H, S and CNOT — that turn every Pauli operator into another Pauli operator.