# TwoQubitBasisDecomposer

`qiskit.quantum_info.TwoQubitBasisDecomposer(gate, basis_fidelity=1.0, euler_basis='U', pulse_optimize=None)`

GitHub(opens in a new tab)

Bases: `object`

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A class for decomposing 2-qubit unitaries into minimal number of uses of a 2-qubit basis gate.

**Parameters**

**gate**(*Gate*) – Two-qubit gate to be used in the KAK decomposition.**basis_fidelity**(*float*(opens in a new tab)) – Fidelity to be assumed for applications of KAK Gate. Default 1.0.**euler_basis**(*str*(opens in a new tab)) – Basis string to be provided to OneQubitEulerDecomposer for 1Q synthesis. Valid options are [‘ZYZ’, ‘ZXZ’, ‘XYX’, ‘U’, ‘U3’, ‘U1X’, ‘PSX’, ‘ZSX’, ‘RR’].**pulse_optimize**(*None or**bool*(opens in a new tab)) – If True, try to do decomposition which minimizes local unitaries in between entangling gates. This will raise an exception if an optimal decomposition is not implemented. Currently, only [{CX, SX, RZ}] is known. If False, don’t attempt optimization. If None, attempt optimization but don’t raise if unknown.

## Methods

### decomp0

`static decomp0(target)`

Decompose target ~Ud(x, y, z) with 0 uses of the basis gate. Result Ur has trace: $|Tr(Ur.Utarget^dag)| = 4|(cos(x)cos(y)cos(z)+ j sin(x)sin(y)sin(z)|$, which is optimal for all targets and bases

### decomp1

`decomp1(target)`

Decompose target ~Ud(x, y, z) with 1 uses of the basis gate ~Ud(a, b, c). Result Ur has trace: .. math:

`|Tr(Ur.Utarget^dag)| = 4|cos(x-a)cos(y-b)cos(z-c) + j sin(x-a)sin(y-b)sin(z-c)|`

which is optimal for all targets and bases with z==0 or c==0

### decomp2_supercontrolled

`decomp2_supercontrolled(target)`

Decompose target ~Ud(x, y, z) with 2 uses of the basis gate.

For supercontrolled basis ~Ud(pi/4, b, 0), all b, result Ur has trace .. math:

`|Tr(Ur.Utarget^dag)| = 4cos(z)`

which is the optimal approximation for basis of CNOT-class `~Ud(pi/4, 0, 0)`

or DCNOT-class `~Ud(pi/4, pi/4, 0)`

and any target. May be sub-optimal for b!=0 (e.g. there exists exact decomposition for any target using B `B~Ud(pi/4, pi/8, 0)`

, but not this decomposition.) This is an exact decomposition for supercontrolled basis and target `~Ud(x, y, 0)`

. No guarantees for non-supercontrolled basis.

### decomp3_supercontrolled

`decomp3_supercontrolled(target)`

Decompose target with 3 uses of the basis. This is an exact decomposition for supercontrolled basis ~Ud(pi/4, b, 0), all b, and any target. No guarantees for non-supercontrolled basis.

### num_basis_gates

`num_basis_gates(unitary)`

Computes the number of basis gates needed in a decomposition of input unitary

### traces

`traces(target)`

Give the expected traces $|Tr(U \cdot Utarget^dag)|$ for different number of basis gates.