def S2Proj(Quket, Q, threshold=1e-8): """Function Perform spin-projection to QuantumState |Q> |Q'> = Ps |Q> where Ps is a spin-projection operator (non-unitary). Ps = \sum_i^ng wg[i] Ug[i] This function provides a shortcut to |Q'>, which is unreal. One actually needs to develop a quantum circuit for this (See PRR 2, 043142 (2020)). Author(s): Takashi Tsuchimochi """ spin = Quket.projection.spin s = (spin - 1) / 2 Ms = Quket.projection.Ms / 2 n_qubits = Q.get_qubit_count() state_P = QuantumState(n_qubits) state_P.multiply_coef(0) nalpha = max(Quket.projection.euler_ngrids[0], 1) nbeta = max(Quket.projection.euler_ngrids[1], 1) ngamma = max(Quket.projection.euler_ngrids[2], 1) for ialpha in range(nalpha): alpha = Quket.projection.sp_angle[0][ialpha] alpha_coef = Quket.projection.sp_weight[0][ialpha] * np.exp( 1j * alpha * Ms) for ibeta in range(nbeta): beta = Quket.projection.sp_angle[1][ibeta] beta_coef = (Quket.projection.sp_weight[1][ibeta] * Quket.projection.dmm[ibeta]) for igamma in range(ngamma): gamma = Quket.projection.sp_angle[2][igamma] gamma_coef = (Quket.projection.sp_weight[2][igamma] * np.exp(1j * gamma * Ms)) # Total Weight coef = (2 * s + 1) / (8 * np.pi) * (alpha_coef * beta_coef * gamma_coef) state_g = QuantumState(n_qubits) state_g.load(Q) circuit_Rg = QuantumCircuit(n_qubits) set_circuit_Rg(circuit_Rg, n_qubits, alpha, beta, gamma) circuit_Rg.update_quantum_state(state_g) state_g.multiply_coef(coef) state_P.add_state(state_g) # Normalize norm2 = state_P.get_squared_norm() if norm2 < threshold: error( "Norm of spin-projected state is too small!\n", "This usually means the broken-symmetry state has NO component ", "of the target spin.") state_P.normalize(norm2) # print_state(state_P,name="P|Q>",threshold=1e-6) return state_P
def NProj(Quket, Q, threshold=1e-8): """Function Perform number-projection to QuantumState |Q> |Q'> = PN |Q> where PN is a number-projection operator (non-unitary). PN = \sum_i^ng wg[i] Ug[i] This function provides a shortcut to |Q'>, which is unreal. One actually needs to develop a quantum circuit for this (See QST 6, 014004 (2021)). Author(s): Takashi Tsuchimochi """ n_qubits = Q.get_qubit_count() state_P = QuantumState(n_qubits) state_P.multiply_coef(0) state_g = QuantumState(n_qubits) nphi = max(Quket.projection.number_ngrids, 1) #print_state(Q) for iphi in range(nphi): coef = (Quket.projection.np_weight[iphi] * np.exp(1j * Quket.projection.np_angle[iphi] * (Quket.projection.n_active_electrons - Quket.projection.n_active_orbitals))) state_g = Q.copy() circuit = QuantumCircuit(n_qubits) set_circuit_ExpNa(circuit, n_qubits, Quket.projection.np_angle[iphi]) set_circuit_ExpNb(circuit, n_qubits, Quket.projection.np_angle[iphi]) circuit.update_quantum_state(state_g) state_g.multiply_coef(coef) state_P.add_state(state_g) norm2 = state_P.get_squared_norm() if norm2 < threshold: error( "Norm of number-projected state is too small!\n", "This usually means the broken-symmetry state has NO component ", "of the target number.") state_P.normalize(norm2) return state_P