Qiskit gates: Support GlobalPhaseGate (#380)

* update sampler docstring

* Qiskit gates: Support GlobalPhaseGate

Author: kevinsung

python/ffsim/qiskit/sampler.py

@@ -60,14 +60,18 @@ def __init__(
 
         2. Use Qiskit gates. The circuit should begin with some ``X`` gates. Next, a
         number of unitary gates are applied. The following unitary gates are supported:
-        [``CPhaseGate``, ``PhaseGate``, ``RZGate``, ``RZZGate``, ``SwapGate``,
-        ``XXPlusYYGate``].
+        [``CPhaseGate``, ``CZGate``, ``GlobalPhaseGate``, ``iSwapGate``, ``PhaseGate``,
+        ``RZGate``, ``RZZGate``, ``SGate``, ``SdgGate``, ``SwapGate``, ``TGate``,
+        ``TdgGate``, ``XXPlusYYGate``, ``ZGate``].
         Finally, measurement gates must only occur at the end of the circuit.
 
         When simulating spinful circuits constructed from Qiskit gates, you should
         pass the `norb` and `nelec` arguments to the FfsimSampler initialization.
         Otherwise, a spinless simulation will be performed, which is less efficient.
 
+        Currently, spinless circuits are limited to 64 qubits, and spinful circuits are
+        limited to 128 qubits.
+
         Args:
             default_shots: The default shots to use if not specified during run.
             norb: The number of spatial orbitals.

python/ffsim/qiskit/sim.py

@@ -22,6 +22,7 @@
     Barrier,
     CPhaseGate,
     CZGate,
+    GlobalPhaseGate,
     Measure,
     PhaseGate,
     RZGate,
@@ -183,7 +184,7 @@ def _evolve_state_vector_spinless(
 ) -> states.StateVector:
     op = instruction.operation
     qubit_indices = [circuit.find_bit(qubit).index for qubit in instruction.qubits]
-    consecutive_sorted = qubit_indices == list(
+    consecutive_sorted = not qubit_indices or qubit_indices == list(
         range(min(qubit_indices), max(qubit_indices) + 1)
     )
     vec = state_vector.vec
@@ -337,6 +338,11 @@ def _evolve_state_vector_spinless(
         )
         return states.StateVector(vec=vec, norb=norb, nelec=nelec)
 
+    if isinstance(op, GlobalPhaseGate):
+        (phase,) = op.params
+        vec *= cmath.rect(1, phase)
+        return states.StateVector(vec=vec, norb=norb, nelec=nelec)
+
     raise ValueError(f"Unsupported gate for spinless circuit: {op}.")
 
 
@@ -347,7 +353,7 @@ def _evolve_state_vector_spinful(
 ) -> states.StateVector:
     op = instruction.operation
     qubit_indices = [circuit.find_bit(qubit).index for qubit in instruction.qubits]
-    consecutive_sorted = qubit_indices == list(
+    consecutive_sorted = not qubit_indices or qubit_indices == list(
         range(min(qubit_indices), max(qubit_indices) + 1)
     )
     vec = state_vector.vec
@@ -604,6 +610,11 @@ def _evolve_state_vector_spinful(
         )
         return states.StateVector(vec=vec, norb=norb, nelec=nelec)
 
+    if isinstance(op, GlobalPhaseGate):
+        (phase,) = op.params
+        vec *= cmath.rect(1, phase)
+        return states.StateVector(vec=vec, norb=norb, nelec=nelec)
+
     raise ValueError(f"Unsupported gate for spinful circuit: {op}.")
 
 

tests/python/qiskit/sim_test.py

@@ -21,6 +21,7 @@
 from qiskit.circuit.library import (
     CPhaseGate,
     CZGate,
+    GlobalPhaseGate,
     PhaseGate,
     RZGate,
     RZZGate,
@@ -204,6 +205,7 @@ def test_qiskit_gates_spinful(norb: int, nelec: tuple[int, int]):
         )
         circuit.append(SwapGate(), [qubits[i], qubits[j]])
         circuit.append(SwapGate(), [qubits[norb + i], qubits[norb + j]])
+    circuit.append(GlobalPhaseGate(rng.uniform(-10, 10)))
 
     # Compute state vector using ffsim
     ffsim_vec = ffsim.qiskit.final_state_vector(circuit, norb=norb, nelec=nelec)
@@ -258,6 +260,7 @@ def test_qiskit_gates_spinless(norb: int, nocc: int):
         )
     for i, j in pairs:
         circuit.append(SwapGate(), [qubits[i], qubits[j]])
+    circuit.append(GlobalPhaseGate(rng.uniform(-10, 10)))
 
     # Compute state vector using ffsim
     ffsim_vec = ffsim.qiskit.final_state_vector(circuit, norb=norb, nelec=nocc)