It works? but slowly
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8 changed files with 420 additions and 28 deletions
252
src/tf-qas.py
Executable file
252
src/tf-qas.py
Executable file
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#!/usr/bin/env python
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from dataclasses import dataclass
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from enum import IntEnum
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import math
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import random
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import numpy as np
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from typing import assert_type, override
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from qiskit.circuit import ParameterVector
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from tqdm import tqdm
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from qiskit import QuantumCircuit as QiskitCircuit, transpile
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from qiskit_aer import AerSimulator
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from qas_flow import Stream
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TWO_QUBIT_GATE_PROBABILITY = 0.5
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class GateType(IntEnum):
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RX = 1
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RY = 2
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RZ = 3
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XX = 4
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YY = 5
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ZZ = 6
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@dataclass(frozen=True)
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class Gate:
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type: GateType
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qubits: int | tuple[int, int]
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param_idx: int
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def haar_fidelity_pdf(F: np.ndarray, d: int) -> np.ndarray:
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# p(F) = (d-1) * (1-F)^(d-2), for F in [0,1]
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return (d - 1) * np.power(1.0 - F, d - 2)
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def kl_divergence(p: np.ndarray, q: np.ndarray) -> float:
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# assumes p, q are normalized and strictly positive
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return float(np.sum(p * np.log(p / q)))
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@dataclass()
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class QuantumCircuit:
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qubits: int
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gates: list[list[Gate]]
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single_qubit_gates: int
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two_qubit_gates: int
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params: int
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paths: int = 0
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expressibility: float = -10000.0
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def calculate_paths(self):
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path_counts = [1 for _ in range(self.qubits)]
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for layer in self.gates:
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for gate in layer:
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if gate.type <= 3 or type(gate.qubits) is int:
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continue
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(q1, q2) = gate.qubits
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path_counts[q1] = path_counts[q1] + path_counts[q2]
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path_counts[q2] = path_counts[q1]
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self.paths = sum(path_counts)
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def to_qiskit(self):
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qc = QiskitCircuit(self.qubits)
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thetas = ParameterVector("theta", self.params)
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for layer in self.gates:
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for gate in layer:
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theta = thetas[gate.param_idx]
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if gate.type == GateType.RX:
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qc.rx(theta, gate.qubits)
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elif gate.type == GateType.RY:
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qc.ry(theta, gate.qubits)
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elif gate.type == GateType.RZ:
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qc.rz(theta, gate.qubits)
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elif gate.type == GateType.XX:
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qc.rxx(theta, *gate.qubits)
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elif gate.type == GateType.YY:
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qc.ryy(theta, *gate.qubits)
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elif gate.type == GateType.ZZ:
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qc.rzz(theta, *gate.qubits)
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qc.save_statevector()
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return qc, thetas
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def expressibility_estimate(
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self, samples: int, seed: int, bins: int = 75, eps: float = 1e-12
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):
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qc, thetas = self.to_qiskit()
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if self.params <= 0:
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return float("inf")
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rng = random.Random(seed)
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d = 1 << self.qubits
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backend = AerSimulator(method="statevector", seed_simulator=seed)
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tqc = transpile(qc, backend)
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# 1) build 2*samples parameterized circuits (left+right)
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binds = []
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for _ in range(2 * samples):
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binds.append(
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{thetas: [rng.random() for _ in range(self.params)]}
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) # SAFE binding
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# 2) compute statevectors (no backend/job overhead)
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job = backend.run(
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[tqc.assign_parameters(bind, inplace=False) for bind in binds]
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)
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result = job.result()
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sv = [result.get_statevector(i) for i in range(len(binds))]
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left = sv[:samples]
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right = sv[samples:]
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# 3) fidelities F = |<ψ|φ>|^2
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inners = np.array(
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[l.inner(r) for l, r in zip(left, right)], dtype=np.complex128
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)
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F = (inners * inners.conjugate()).real
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F = np.clip(F, 0.0, 1.0) # numerical safety
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# 4) empirical histogram (as a probability mass over bins)
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hist, edges = np.histogram(F, bins=bins, range=(0.0, 1.0), density=False)
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p = hist.astype(np.float64)
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p = p + eps
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p = p / p.sum()
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# 5) Haar distribution mass per bin (integrate PDF over each bin)
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# approximate via midpoint rule
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mids = 0.5 * (edges[:-1] + edges[1:])
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widths = edges[1:] - edges[:-1]
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q = haar_fidelity_pdf(mids, d) * widths
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q = q + eps
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q = q / q.sum()
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kl = kl_divergence(p, q)
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self.expressibility = kl
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return kl
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@override
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def __str__(self):
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strs = ["-" for _ in range(self.qubits)]
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for layer in self.gates:
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for i in range(self.qubits):
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strs[i] += "---"
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idx = 0
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for gate in layer:
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match gate.type:
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case GateType.RX:
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strs[gate.qubits] = strs[gate.qubits][:-2] + "RX"
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case GateType.RY:
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strs[gate.qubits] = strs[gate.qubits][:-2] + "RY"
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case GateType.RZ:
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strs[gate.qubits] = strs[gate.qubits][:-2] + "RZ"
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case GateType.XX:
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(q1, q2) = gate.qubits
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strs[q1] = strs[q1][:-2] + f"X{idx}"
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strs[q2] = strs[q2][:-2] + f"X{idx}"
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idx += 1
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case GateType.YY:
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(q1, q2) = gate.qubits
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strs[q1] = strs[q1][:-2] + f"Y{idx}"
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strs[q2] = strs[q2][:-2] + f"Y{idx}"
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idx += 1
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case GateType.ZZ:
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(q1, q2) = gate.qubits
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strs[q1] = strs[q1][:-2] + f"Z{idx}"
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strs[q2] = strs[q2][:-2] + f"Z{idx}"
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idx += 1
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return (
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"\n".join(strs)
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+ f"\npaths: {self.paths}, expressibility: {self.expressibility}"
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)
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def even_parity(qubits: int):
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return [(x, x + 1) for x in range(0, qubits, 2)]
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def odd_parity(qubits: int):
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return [(x, x + 1) for x in range(1, qubits, 2)]
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def sample_circuit(rng: random.Random, qubits: int, depth: int) -> QuantumCircuit:
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even = even_parity(qubits)
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odd = odd_parity(qubits)
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total_single = 0
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total_double = 0
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params = 0
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gates: list[list[Gate]] = []
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for _ in range(depth):
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gate_type_offset = 3 if rng.random() < TWO_QUBIT_GATE_PROBABILITY else 0
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gate_type = rng.randint(1, 3)
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gate_locations = even if rng.random() < 0.5 else odd
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if gate_type_offset == 0:
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gates.append(
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[Gate(GateType(gate_type), x, params) for (x, _) in gate_locations]
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)
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total_single += len(gate_locations)
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else:
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gates.append(
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[
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Gate(GateType(gate_type + gate_type_offset), xy, params)
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for xy in gate_locations
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if xy[1] != qubits
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]
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)
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total_double += len(gate_locations)
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params += 1
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return QuantumCircuit(qubits, gates, total_single, total_double, params)
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def sample_generator(rng: random.Random, qubits: int, depth: int):
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while True:
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yield sample_circuit(rng, qubits, depth)
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def more_single_than_double(qc: QuantumCircuit) -> bool:
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return qc.single_qubit_gates >= qc.two_qubit_gates
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if __name__ == "__main__":
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rng = random.Random()
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qubits = 6
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depth = 10
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sample_amount = 50000
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expressibility_samples = 2000
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proxy_pass_amount = 5000
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circuits = (
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Stream(sample_generator(rng, qubits, depth))
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.filter(more_single_than_double)
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.take(sample_amount)
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.collect()
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)
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for circuit in tqdm(circuits):
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circuit.calculate_paths()
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circuits.sort(key=lambda qc: qc.paths, reverse=True)
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for circuit in tqdm(circuits[:proxy_pass_amount]):
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circuit.expressibility_estimate(
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expressibility_samples, rng.randint(0, 100000000)
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)
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circuits.sort(key=lambda qc: qc.expressibility)
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for i, circuit in enumerate(circuits[:proxy_pass_amount]):
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print(f"circuit {i}:\n{circuit}")
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