Using backends

In SolverConfig, we can specify the backend to use when using a quantum approach, that is how we perform quantum runs. Several backends and devices are available via Qooqit.

Backend configuration

The backend configuration part in SolverConfig is set via two fields.

Field	Type	Description
backend	LocalEmulator | RemoteEmulator | QPU	(optional) Which backend to use.
device	Device	(optional) The quantum device specification. Defaults to DigitalAnalogDevice.

Local backends

Local backends perform simulations locally. The main available backends are:

• qutip using the Qutip simulator as the default,
• emu_mps: emulator based on state of the art tensor network techniques,
• emu_sv: emulator based on state-vector description.

To use any, simply instantiate a SolverConfig with the backend attribute as a LocalEmulator. We can specify the number of shots via the runs attribute and configure differently the backend. See Qoolqit for more details.

from qubosolver.config import SolverConfig, LocalEmulator
from pulser_simulation import QutipBackendV2
from emu_sv import SVBackend
from emu_mps import MPSBackend
from qoolqit import DigitalAnalogDevice

locals_bkds = [
    LocalEmulator(backend_type=btype, runs=500)
    for btype in [
        QutipBackendV2,
        SVBackend,
        MPSBackend,
    ]
]


config = SolverConfig(
    use_quantum=True,
    backend=locals_bkds[0],
    device=DigitalAnalogDevice(),
)

Alternatively use the SolverConfig.from_kwargs method:

from qubosolver.config import SolverConfig, LocalEmulator
from pulser_simulation import QutipBackendV2
from emu_sv import SVBackend
from emu_mps import MPSBackend
from qoolqit import DigitalAnalogDevice

locals_bkds = [
    LocalEmulator(backend_type=btype, runs=500)
    for btype in [
        QutipBackendV2,
        SVBackend,
        MPSBackend,
    ]
]

config = SolverConfig.from_kwargs(
    use_quantum=True,
    backend=locals_bkds[0],
    device=DigitalAnalogDevice(),
)

Remote backends

Remote backends submit jobs to a remote server via pasqal-cloud. For this, we require specifying a RemoteEmulator or QPU and connection details. Using the code below, replace with your username, project id and password on the Pasqal Cloud.

from qubosolver.config import SolverConfig, PasqalCloud, RemoteEmulator
from pulser_pasqal.backends import EmuFreeBackendV2, EmuMPSBackend

USERNAME="#TO_PROVIDE"
PROJECT_ID="#TO_PROVIDE"
PASSWORD=None

if PASSWORD is not None:
    connection = PasqalCloud(
        username=USERNAME,
        password=PASSWORD,
        project_id=PROJECT_ID,
    )
    remote_emulators = [RemoteEmulator(backend_type=btype, connection=connection, runs=500)
    for btype in [
        EmuFreeBackendV2,
        EmuMPSBackend,
    ]]
    config = SolverConfig(
        use_quantum=True,
        backend = remote_emulators[0],
    )

We can also target a remote QPU as follows:

import qoolqit
from qubosolver.config import SolverConfig, PasqalCloud, QPU
from pulser_pasqal.backends import EmuFreeBackendV2, EmuMPSBackend

USERNAME="#TO_PROVIDE"
PROJECT_ID="#TO_PROVIDE"
PASSWORD=None

if PASSWORD is not None:
    connection = PasqalCloud(
        username=USERNAME,
        password=PASSWORD,
        project_id=PROJECT_ID,
    )
    # specify the QPU device
    device = qoolqit.devices.Device(pulser_device=connection.fetch_available_devices()["FRESNEL"])
    config = SolverConfig(
        use_quantum=True,
        backend = QPU(connection=connection, runs=500), device=device,
    )