# XXDecomposer

`qiskit.synthesis.XXDecomposer(basis_fidelity=1.0, euler_basis='U', embodiments=None, backup_optimizer=None)`

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A class for optimal decomposition of 2-qubit unitaries into 2-qubit basis gates of `XX`

type (i.e., each locally equivalent to $CAN(\alpha, 0, 0)$ for a possibly varying $alpha$).

**Parameters**

**basis_fidelity**(*dict*(opens in a new tab)*|**float*(opens in a new tab)) – available strengths and fidelity of each. Can be either (1) a dictionary mapping`XX`

angle values to fidelity at that angle; or (2) a single float`f`

, interpreted as`{pi: f, pi/2: f/2, pi/3: f/3}`

.**euler_basis**(*str*(opens in a new tab)) – Basis string provided to`OneQubitEulerDecomposer`

for 1Q synthesis. Defaults to`"U"`

.**embodiments**(*dict*(opens in a new tab)*[**float*(opens in a new tab)*,**QuantumCircuit**] | None*) – A dictionary mapping interaction strengths alpha to native circuits which embody the gate $CAN(\alpha, 0, 0)$. Strengths are taken so that $pi/2$ represents the class of a full`CXGate`

.**backup_optimizer**(*Callable[...,**QuantumCircuit**] | None*) – If supplied, defers synthesis to this callable when`XXDecomposer`

has no efficient decomposition of its own. Useful for special cases involving 2 or 3 applications of $XX(\pi/2)$, in which case standard synthesis methods provide lower 1Q gate count.

Note

If `embodiments`

is not passed, or if an entry is missing, it will be populated as needed using the method `_default_embodiment`

.

## Methods

### num_basis_gates

`num_basis_gates(unitary)`

Counts the number of gates that would be emitted during re-synthesis.

Note

This method is used by `ConsolidateBlocks`

.

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