Entanglement view

Starting from server version 1.0.26, Quantag Studio provides an Entanglement section in the Variables panel during circuit debugging.

After executing a step (F10) or stopping at a breakpoint, two variable groups are shown:

  • Quantum State – amplitudes of the current quantum state

  • Entanglement – quantitative entanglement information

Entanglement view

What is shown in Entanglement

For each qubit qi, the entanglement section shows a value:

S_qi

where S_qi is the von Neumann entropy of qubit qi with respect to the rest of the system.

Interpretation:

  • S_qi = 0.0 – the qubit is not entangled (separable state)

  • 0.0 < S_qi < 1.0 – the qubit is partially entangled

  • S_qi ≈ 1.0 – the qubit is maximally entangled with the rest of the system

The following summary values may also be displayed:

S_max   – maximum entanglement among all qubits
S_avg   – average entanglement over all qubits

Notes

  • Entanglement values are updated only when execution stops (step or breakpoint).

  • Entanglement is computed from the current quantum state before measurement.

  • After a measurement operation, entanglement typically collapses to zero.

  • Controlled gates (for example cx) create entanglement only if the control qubit is in superposition.

Example

The following OpenQASM code does not create entanglement:

h q[0];
cx q[1], q[0];

The following code creates entanglement:

h q[0];
cx q[0], q[1];