Layout

class qiskit.transpiler.Layout(input_dict=None)

Bases: object

Two-ways dict to represent a Layout.

construct a Layout from a bijective dictionary, mapping virtual qubits to physical qubits

Methods

add(virtual_bit, physical_bit=None)

Adds a map element between bit and physical_bit. If physical_bit is not defined, bit will be mapped to a new physical bit.

Parameters:

• virtual_bit (tuple) – A (qu)bit. For example, (QuantumRegister(3, ‘qr’), 2).

• physical_bit (int) – A physical bit. For example, 3.

add_register(reg)

Adds at the end physical_qubits that map each bit in reg.

Parameters:

reg (Register) – A (qu)bit Register. For example, QuantumRegister(3, ‘qr’).

combine_into_edge_map(another_layout)

Combines self and another_layout into an “edge map”.

For example:

   self       another_layout  resulting edge map
qr_1 -> 0        0 <- q_2         qr_1 -> q_2
qr_2 -> 2        2 <- q_1         qr_2 -> q_1
qr_3 -> 3        3 <- q_0         qr_3 -> q_0

The edge map is used to compose dags via, for example, compose.

Parameters:

another_layout (Layout) – The other layout to combine.

Returns:

A “edge map”.

Return type:

dict

Raises:

LayoutError – another_layout can be bigger than self, but not smaller. Otherwise, raises.

copy()

Returns a copy of a Layout instance.

from_dict(input_dict)

Populates a Layout from a dictionary.

The dictionary must be a bijective mapping between virtual qubits (tuple) and physical qubits (int).

Parameters:

input_dict (dict) –

e.g.:

{(QuantumRegister(3, 'qr'), 0): 0,
 (QuantumRegister(3, 'qr'), 1): 1,
 (QuantumRegister(3, 'qr'), 2): 2}

Can be written more concisely as follows:

* virtual to physical::

    {qr[0]: 0,
     qr[1]: 1,
     qr[2]: 2}

* physical to virtual::

    {0: qr[0],
     1: qr[1],
     2: qr[2]}

static from_intlist(int_list, *qregs)

Converts a list of integers to a Layout mapping virtual qubits (index of the list) to physical qubits (the list values).

Parameters:

• int_list (list) – A list of integers.

• *qregs (QuantumRegisters) – The quantum registers to apply the layout to.

Returns:

The corresponding Layout object.

Return type:

Layout

Raises:

LayoutError – Invalid input layout.

static from_qubit_list(qubit_list, *qregs)

Populates a Layout from a list containing virtual qubits, Qubit or None.

Parameters:

• qubit_list (list) – e.g.: [qr[0], None, qr[2], qr[3]]

• *qregs (QuantumRegisters) – The quantum registers to apply the layout to.

Returns:

the corresponding Layout object

Return type:

Layout

Raises:

LayoutError – If the elements are not Qubit or None

static generate_trivial_layout(*regs)

Creates a trivial (“one-to-one”) Layout with the registers and qubits in regs.

Parameters:

*regs (Registers, Qubits) – registers and qubits to include in the layout.

Returns:

A layout with all the regs in the given order.

Return type:

Layout

get_physical_bits()

Returns the dictionary where the keys are physical (qu)bits and the values are virtual (qu)bits.

get_registers()

Returns the registers in the layout [QuantumRegister(2, ‘qr0’), QuantumRegister(3, ‘qr1’)] :returns: A set of Registers in the layout :rtype: Set

get_virtual_bits()

Returns the dictionary where the keys are virtual (qu)bits and the values are physical (qu)bits.

static order_based_on_type(value1, value2)

decides which one is physical/virtual based on the type. Returns (virtual, physical)

reorder_bits(bits)

Given an ordered list of bits, reorder them according to this layout.

The list of bits must exactly match the virtual bits in this layout.

Parameters:

bits (list[Bit]) – the bits to reorder.

Returns:

ordered bits.

Return type:

List

swap(left, right)

Swaps the map between left and right.

Parameters:

• left (tuple or int) – Item to swap with right.

• right (tuple or int) – Item to swap with left.

Raises:

LayoutError – If left and right have not the same type.