qpe_toolbox.circuit.controls

Routines for quimb circuits and/or gates.

Functions

shift_control_gates(gates, m_aux, k_ctrl)

Shift gate targets and controls to account for an auxiliary qubit register.

Module Contents

qpe_toolbox.circuit.controls.shift_control_gates(gates, m_aux, k_ctrl)[source]

Shift gate targets and controls to account for an auxiliary qubit register.

This function is used when an auxiliary (ancilla) register occupies the first m_aux qubits of a circuit. All gates acting on the data register are shifted by m_aux in their qubit indices, and an additional control qubit from the auxiliary register is added to each gate.

Parameters:

  • gates (iterable of Gate) – List of gates to shift.

  • m_aux (int) – Number of auxiliary qubits occupying the lowest indices [0, m_aux - 1].

  • k_ctrl (int) – Index of the control qubit within the auxiliary register. Must satisfy 0 <= k_ctrl < m_aux.

Returns:

controlled_gates – New list of gate objects with shifted qubit indices and added control.

Return type:

list of Gate

Raises:

ValueError – If k_ctrl lies outside the auxiliary register.

Notes

  • Target qubits q are mapped to q + m_aux.

  • Existing control qubits are also shifted by m_aux.

  • If a gate originally has no controls, it becomes singly controlled by k_ctrl.

  • The original gate objects are not modified.