I’m implementing Grover minimum finding in Qiskit. Can someone help me debug this code?

I’m implementing Grover minimum finding in Qiskit. Can someone help me debug this code? Ask Question Asked today Modified today Viewed 21 times 0 import random import math import numpy as np from qiskit import QuantumCircuit, QuantumRegister, ClassicalRegister, transpile from qiskit.circuit.library import MCMTGate, ZGate, MCXGate from qiskit_aer import Aer, AerSimulator maximum_number_qubits_key = 5 number_qubits_qc = random.randint(2, maximum_number_qubits_key) total_trials = 10 print(number_qubits_qc) def generate_initial_state(): keys = list(range(0, 2**number_qubits_qc)) values = random.sample(range(0, 2**number_qubits_qc), k=2**number_qubits_qc) result = dict(zip(keys, values)) print(result) return result def build_grover_oracle(marked_states): num_qubits = len(marked_states[0]) qc = QuantumCircuit(num_qubits) for target in marked_states: rev_target = target[::-1] zero_inds = [ ind for ind in range(num_qubits) if rev_target[ind] == '0' ] if zero_inds: qc.x(zero_inds) qc.compose(MCMTGate(ZGate(), num_qubits - 1, 1), inplace=True) if zero_inds: qc.x(zero_inds) return qc def build_grover_diffuser(n_qubits): qc = QuantumCircuit(n_qubits) qc.h(range(n_qubits)) qc.x(range(n_qubits)) qc.h(n_qubits - 1) qc.append(MCXGate(n_qubits - 1), list(range(n_qubits))) qc.h(n_qubits - 1) qc.x(range(n_qubits)) qc.h(range(n_qubits)) return qc.to_gate(label='Diffuser') def build_grover_operator(oracle): n_qubits = oracle.num_qubits oracle_gate = oracle.to_gate(label='Oracle') diffuser = build_grover_diffuser(n_qubits) grover = QuantumCircuit(n_qubits) grover.append(oracle_gate, range(n_qubits)) grover.append(diffuser, range(n_qubits)) return grover.to_gate(label='Grover') def grover_search(targets, N, shots=8192): marked_states = [format(target, f'0{number_qubits_qc}b') for target in targets] oracle = build_grover_oracle(marked_states) grover_op = build_grover_operator(oracle) qc = QuantumCircuit(number_qubits_qc, number_qubits_qc) qc.h(range(number_qubits_qc)) M = len(targets) r = max(1, int(np.floor((np.pi / 4) * np.sqrt(N / M)))) for _ in range(r): qc.append(grover_op, range(number_qubits_qc)) qc.measure(range(number_qubits_qc), range(number_qubits_qc)) backend = Aer.get_backend("qasm_simulator") tqc = transpile(qc, backend) counts = backend.run(tqc, shots=shots).result().get_counts() valid_counts = {} for bitstring, count in counts.items(): idx = int(bitstring[::-1], 2) if idx in targets: valid_counts[idx] = valid_counts.get(idx, 0) + count if valid_counts: return max(valid_counts, key=valid_counts.get) return grover_search(targets, N, shots=shots) def find_min_key_grover(initial_state): N = len(initial_state) nums = [initial_state[i] for i in range(N)] iters = max(1, 2 * math.ceil(np.sqrt(N))) best_idx = random.randint(0, N - 1) best_val = nums[best_idx] for _ in range(iters): targets = [i for i in range(N) if nums[i] < best_val] if not targets: break candidate_idx = grover_search(targets, N) candidate_val = nums[candidate_idx] if candidate_val < best_val: best_idx = candidate_idx best_val = candidate_val return best_idx def generate_qc_for_gmf(initial_state): min_key = find_min_key_grover(initial_state) encoded_value = int(str(min_key), 16) n_qubits = max(1, encoded_value.bit_length()) q = QuantumRegister(n_qubits, "q") c = ClassicalRegister(n_qubits, "c") qc = QuantumCircuit(q, c) bitstring = format(encoded_value, f"0{n_qubits}b")[::-1] for i, bit in enumerate(bitstring): if bit == '1': qc.x(q[i]) qc.measure(q, c) return qc all_ok = True for index_trial in range(total_trials): initial_state = generate_initial_state() qc = generate_qc_for_gmf(initial_state) min_key = str(min(initial_state, key=initial_state.get)) shots = 8192 result = AerSimulator(method='statevector', shots=shots).run(qc).result().data()['counts'] qc_min_key = str(min(result, key=result.get).replace('0x', '')) if min_key == qc_min_key: print('✔️ Trial', index_trial + 1, 'is correct. Min key:', min_key, 'QC min key:', qc_min_key) else: all_ok = False print('❌ Trial', index_trial + 1, 'is NOT correct. Min key:', min_key, 'QC min key:', qc_min_key) if all_ok: print() print('🎉 CONGRATULATIONS YOU COMPLETED THE EXERCISE') else: print() print('💥 THERE IS A PROBLEM. KEEP TRYING!') ``` qiskitquantum-algorithmsgrovers-algorithm Share Improve this question Follow edited 1 hour ago Amazon Dies In Darkness 1051 1 gold badge 1 1 silver badge 4 4 bronze badges asked 4 hours ago Lass 11 1 bronze badge New contributor Hi and welcome to QCSE! Can you add more details to your post? In particular, what you're trying to accomplish, what you expect to see and what you actually get? This well make helping you much easier. –  Tristan Nemoz ♦ Commented 4 hours ago Hi What I want to do is generate a random dictionary of key pairs, where keys go from 0 to (2^n-1) and values are a random permutation of the same range. Use a custom Grover oracle + diffuser to repeatedly search for indices whose value is smaller than the current best value. Return the key corresponding to the minimum value. The main issue is that sometimes the code gets stuck and eventually times out. –  Lass Commented 2 hours ago You might need to provide more details. When does it time out? is it when you have a large number of qubits? If so, then it might be just the fact that the circuits are too big for your computer to handle. I ran your code and didn't see issues until I got to about 10-11 qubits, which is not unreasonable. –  diemilio Commented 56 mins ago Add a comment Know someone who can answer? Share a link to this question via email, Twitter, or Facebook. Your Answer Sign up or log in Sign up using Google Sign up using Email and Password Post as a guest Name Email Required, but never shown Post Your Answer By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy. 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