# cirq.decompose_two_qubit_interaction_into_four_fsim_gates_via_b¶

cirq.decompose_two_qubit_interaction_into_four_fsim_gates_via_b(interaction: Union[cirq.Operation, cirq.Gate, numpy.ndarray, Any], *, fsim_gate: Union[cirq.FSimGate, cirq.ISwapPowGate], qubits: Sequence[cirq.Qid] = None)cirq.Circuit[source]

Decomposes operations into an FSimGate near theta=pi/2, phi=0.

This decomposition is guaranteed to use exactly four of the given FSim
gates. It works by decomposing into two B gates and then decomposing each
B gate into two of the given FSim gate.
This decomposition only works for FSim gates with a theta (iswap angle)
between 3/8π and 5/8π (i.e. within 22.5° of maximum strength) and a
phi (cphase angle) between -π/4 and +π/4 (i.e. within 45° of minimum
strength).
Parameters
• interaction – The two qubit operation to synthesize. This can either be a cirq object (such as a gate, operation, or circuit) or a raw numpy array specifying the 4x4 unitary matrix.

• fsim_gate – The only two qubit gate that is permitted to appear in the output. Must satisfy 3/8π < phi < 5/8π and abs(theta) < pi/4.

• qubits – The qubits that the resulting operations should apply the desired interaction to. If not set then defaults to either the qubits of the given interaction (if it is a cirq.Operation) or else to cirq.LineQubit.range(2).

Returns

A list of operations implementing the desired two qubit unitary. The list will include four operations of the given fsim gate, various single qubit operations, and a global phase operation.