Initial Phaser port

examples/analog/gradients.py

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+# This example shows how to calculate gradients
+from __future__ import annotations
+
+import jax
+import jax.numpy as jnp
+from jax import random
+from phaser import simulate
+from phaser.models import RydbergHamiltonian
+from phaser.utils import init_state
+
+key = random.PRNGKey(42)
+
+# Initializing Hamiltonian
+n_qubits = 15
+dt, N = 1e-3, 3000
+laser_params = (1.0, 2.0)
+U = jnp.triu(random.normal(key, (n_qubits, n_qubits)) ** 2)
+in_state = init_state(n_qubits)
+
+
+def laser(laser_params, t):
+    (w_rabi, w_detune) = laser_params
+    return {
+        "rabi": 20.0 * jnp.cos(2 * jnp.pi * w_rabi * t),
+        "detune": 15.0 * jnp.cos(2 * jnp.pi * w_detune * t),
+    }
+
+
+hamiltonian = RydbergHamiltonian(n_qubits, U)
+hamiltonian_params = hamiltonian.init(
+    key,
+    in_state,
+    laser(laser_params, 0),
+)
+
+
+# We take the gradient of some random state w.r.t the laser params and interaction_matrix
+def forward(laser_params, hamiltonian_params):
+    out_state = simulate(
+        hamiltonian,
+        hamiltonian_params,
+        laser,
+        laser_params,
+        N,
+        dt,
+        in_state,
+    )
+    return (jnp.abs(out_state) ** 2).flatten()[-1]
+
+
+# Getting the gradient fn w.r.t. both the pulse and interaction matrix and printing the grads
+# Note that we jit (compile) the function so the timing here includes compiling
+# but this only needs to happen once
+grad_fn = jax.jit(jax.grad(forward, argnums=[0, 1]))
+laser_grads, interaction_grads = grad_fn(laser_params, hamiltonian_params)
+
+print(f"Gradients w.r.t laser params: \n {laser_grads}")
+print(f"Gradients w.r.t interaction matrix: \n {interaction_grads}")

examples/analog/introduction.py

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+# This example shows how to build a model hamiltonian and simulate it.
+from __future__ import annotations
+
+from time import time
+
+import flax.linen as nn
+import jax.numpy as jnp
+import numpy as np
+from chex import Array
+from jax import random
+from phaser.hamiltonians import Interaction, Number, Pauli_x
+from phaser.propagators import second_order_trotter
+from phaser.simulate import simulate
+from phaser.utils import init_state, kron_sum
+
+key = random.PRNGKey(42)
+
+
+class RydbergHamiltonian(nn.Module):
+    n_qubits: int
+    U: Array
+
+    def setup(self):
+        # Rabi terms
+        H_rabi = [Pauli_x((idx,), None) for idx in np.arange(self.n_qubits)]
+
+        # Detuning terms
+        H_detune = [Number((idx,), None) for idx in np.arange(self.n_qubits)]
+
+        # Interaction term
+        # We don't want to learn U here so it's just a matrix
+        self.U_params = self.U[np.triu_indices_from(self.U, k=1)]
+        H_interact = [Interaction(idx, None) for idx in zip(*np.triu_indices_from(self.U, k=1))]
+
+        # Joining all terms
+        self.H = H_rabi + H_detune + H_interact
+
+    def __call__(self, state, weights):
+        weights = jnp.concatenate([weights["rabi"] / 2, -weights["detune"], self.U_params])
+        return kron_sum(self.H, state, weights)
+
+    def evolve(self, state: Array, dt: float, weights: dict):
+        # Getting weights into same shape
+        weights = jnp.concatenate([weights["rabi"] / 2, -weights["detune"], self.U_params])
+        return second_order_trotter(self.H, state, dt, weights)
+
+
+# Initializing Hamiltonian
+n_qubits = 15
+dt, N = 1e-3, 3000
+laser_params = (1.0, 2.0)
+U = jnp.triu(random.normal(key, (n_qubits, n_qubits)) ** 2)
+in_state = init_state(n_qubits)
+
+
+# We call it laser here but it's just a function which takes in 1) some parameters and 2) the time of the simulation
+# and returns the parameter values of the hamiltonian. So it's really just a way to simulate time dependent hamiltonians.
+def laser(laser_params, t):
+    (w_rabi, w_detune) = laser_params
+    return {
+        "rabi": jnp.full((n_qubits,), 20.0 * jnp.cos(2 * jnp.pi * w_rabi * t)),
+        "detune": jnp.full((n_qubits,), 15.0 * jnp.cos(2 * jnp.pi * w_detune * t)),
+    }
+
+
+hamiltonian = RydbergHamiltonian(n_qubits, U)
+hamiltonian_params = hamiltonian.init(
+    key,
+    in_state,
+    laser(laser_params, 0),
+)
+
+
+# Timing
+start = time()
+_ = simulate(
+    hamiltonian,
+    hamiltonian_params,
+    laser,
+    laser_params,
+    N,
+    dt,
+    in_state,
+).block_until_ready()
+stop = time()
+
+print(f"Simulation time for {n_qubits} qubits and {N} steps: {stop - start}s")
+print("Note that for clarity we didn't jit the final function, so compilation time is included.")

examples/analog/making_efficient_models.py

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+# This shows how to build an efficient model using diagonalization
+from __future__ import annotations
+
+from time import time
+
+import flax.linen as nn
+import jax.numpy as jnp
+import numpy as np
+from chex import Array
+from jax import random
+from phaser.diagonal import diagonal_onebody_hamiltonian, diagonal_twobody_hamiltonian
+from phaser.hamiltonians import HamiltonianTerm, Pauli_x, n
+from phaser.propagators import second_order_trotter
+from phaser.simulate import simulate
+from phaser.utils import init_state, kron_sum
+
+key = random.PRNGKey(42)
+
+
+# Defining diagonal detuning
+def diagonal_detune_H(idx, weights):
+    return diagonal_onebody_hamiltonian(n, weights, idx)
+
+
+def diagonal_detune_expm(idx, weights):
+    return jnp.exp(-1j * diagonal_detune_H(idx, weights))
+
+
+DiagonalDetune = HamiltonianTerm.create(diagonal_detune_H, diagonal_detune_expm)
+
+
+# Interaction
+def diagonal_interaction_H(idx, weights):
+    return diagonal_twobody_hamiltonian((n, n), weights, idx)
+
+
+def diagonal_interaction_expm(idx, weights):
+    return jnp.exp(-1j * diagonal_interaction_H(idx, weights))
+
+
+DiagonalInteraction = HamiltonianTerm.create(diagonal_interaction_H, diagonal_interaction_expm)
+
+
+def generate_interaction(U):
+    U_params = jnp.stack(U[np.triu_indices_from(U, k=1)])
+    idx = tuple(zip(*np.triu_indices_from(U, k=1)))
+
+    return DiagonalInteraction(idx, lambda key: U_params)
+
+
+class DiagonalRydbergHamiltonian(nn.Module):
+    n_qubits: int
+    U: Array
+
+    def setup(self):
+        # Rabi terms
+        H_rabi = [Pauli_x((idx,), None) for idx in range(self.n_qubits)]
+
+        # Detuning
+        H_detune = DiagonalDetune(range(self.n_qubits), None)
+
+        # Interaction term
+        H_interact = generate_interaction(self.U)
+
+        # Joining all terms
+        self.H = [*H_rabi, H_detune, H_interact]
+
+    def __call__(self, state, weights):
+        return kron_sum(self.H, state, self.parse_weights(weights))
+
+    def evolve(self, state: Array, dt: float, weights: dict):
+        return second_order_trotter(self.H, state, dt, self.parse_weights(weights))
+
+    def parse_weights(self, weights):
+        # Parse the weights from tuple to correct shape and values
+        return [
+            *jnp.full((self.n_qubits,), weights["rabi"] / 2),
+            jnp.full((self.n_qubits,), -weights["detune"]),
+            None,
+        ]
+
+
+if __name__ == "__main__":
+    # Initializing Hamiltonian
+    n_qubits = 20
+    dt, N = 1e-3, 3000
+    laser_params = (1.0, 2.0)
+    U = jnp.triu(random.normal(key, (n_qubits, n_qubits)) ** 2)
+    in_state = init_state(n_qubits)
+
+    def laser(laser_params, t):
+        (w_rabi, w_detune) = laser_params
+        return {
+            "rabi": 20.0 * jnp.cos(2 * jnp.pi * w_rabi * t),
+            "detune": 15.0 * jnp.cos(2 * jnp.pi * w_detune * t),
+        }
+
+    hamiltonian = DiagonalRydbergHamiltonian(n_qubits, U)
+    hamiltonian_params = hamiltonian.init(
+        key,
+        in_state,
+        laser(laser_params, 0),
+    )
+
+    # Timing
+    start = time()
+    _ = simulate(
+        hamiltonian,
+        hamiltonian_params,
+        laser,
+        laser_params,
+        N,
+        dt,
+        in_state,
+    ).block_until_ready()
+    stop = time()
+
+    print(f"Simulation time for {n_qubits} qubits and {N} steps: {stop - start}s")
+    print(
+        "Note that for clarity we didn't jit the final function, so compilation time is included."
+    )

horqrux/phaser/__init__.py

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+from __future__ import annotations
+
+from .simulate import simulate

horqrux/phaser/diagonal.py

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+from __future__ import annotations
+
+from functools import reduce
+from itertools import chain
+
+import jax.numpy as jnp
+from chex import Array
+
+from .utils import diagonal_kronecker, kron_AI, kron_IA
+
+
+def diagonal_onebody_hamiltonian(Hi: Array, weights: Array, idx: list[int]) -> Array:
+    # Generates diagonal of diagonal onebody hamiltonian terms.
+    # Not pretty but it works...
+    def diagonal_Hi(diagonal: Array, idx: int) -> Array:
+        return kron_IA(kron_AI(diagonal, 2 ** (n_qubits - idx - 1)), 2**idx)
+
+    n_qubits = max(idx) + 1  # +1 cause of index
+    Hi_diag = jnp.diag(Hi)
+    return reduce(
+        lambda state, x: state + x[0] * diagonal_Hi(Hi_diag, x[1]),
+        zip(weights, idx),
+        jnp.zeros(2**n_qubits),
+    )
+
+
+def diagonal_twobody_hamiltonian(
+    HiHj: tuple[Array, Array], weights: Array, idx: list[tuple[int, int]]
+) -> Array:
+    # Generates diagonal of diagonal two-body hamiltonian terms.
+    # Not pretty but it works...
+    def diagonal_Hi(diagonal: list[Array], idx_ij: tuple[int, int]) -> Array:
+        idx_i, idx_j = idx_ij
+        left = kron_IA(diagonal[0], 2 ** (idx_i))
+        right = kron_IA(kron_AI(diagonal[1], 2 ** (n_qubits - idx_j - 1)), 2 ** (idx_j - idx_i - 1))
+        return diagonal_kronecker(left, right)
+
+    n_qubits = max(list(chain(*idx))) + 1  # +1 cause of index
+    HiHj_diag = [jnp.diag(H) for H in HiHj]
+    return reduce(
+        lambda state, x: state + x[0] * diagonal_Hi(HiHj_diag, x[1]),
+        zip(weights, idx),
+        jnp.zeros(2**n_qubits),
+    )