quchip.devices.transmon.charge_basis

Transmon authored in a finite integer-charge basis.

Classes

ChargeBasisTransmon(E_C, E_J[, n_g, levels, ...])

Transmon with its Hamiltonian authored in the integer-charge basis.

class quchip.devices.transmon.charge_basis.ChargeBasisTransmon(E_C, E_J, n_g=0.0, levels=None, label=None, *, num_basis=61, basis=None, collapse_model='fermi_golden', coupling_channel=None, collapse_rate_threshold=1e-08, **noise)

Bases: DeviceModel

Transmon with its Hamiltonian authored in the integer-charge basis.

The native Hamiltonian is \(4E_C(n-n_g)^2-E_J\cos\varphi\) in ordinary GHz.

Parameters:

• E_C (float) – Positive charging and Josephson energies in GHz.

• E_J (float) – Positive charging and Josephson energies in GHz.

• n_g (float, default 0.0) – Offset charge in Cooper-pair units.

• levels (int or None, default None) – Number of projected eigenstates, required when basis="eigen". None uses the native dimension for the native basis.

• label (str or None, default None) – Device label.

• num_basis (int, keyword-only, default 61) – Odd integer-charge basis size, at least 3.

• basis ({None, "native", "eigen"}, keyword-only) – Requested solver basis. None inherits the chip policy and uses native basis for standalone resolution. native keeps the charge basis, and eigen projects onto levels energy states.

• collapse_model ({"fermi_golden", "ladder"}, default "fermi_golden") – Relaxation construction. When T1 is set, Fermi-golden-rule relaxation requires coupling_channel="charge".

• coupling_channel ({None, "charge"}, default None) – Physical operator for matrix-element relaxation. Only "charge" is supported and selects the authored charge operator \(n\).

• collapse_rate_threshold (float, default 1e-8) – Non-negative dimensionless cutoff on squared matrix-element ratios relative to the selected 0 -> 1 transition.

• T1 (float or None) – Relaxation and dephasing times in ns. None disables each channel.

• T2 (float or None) – Relaxation and dephasing times in ns. None disables each channel.

• thermal_occupation (float or None) – Mean thermal occupation (dimensionless). None disables thermal absorption.

• noise (keyword arguments) – The concrete constructor accepts inherited noise fields as keyword arguments.

References

See Koch et al., Phys. Rev. A 76, 042319 (2007), https://doi.org/10.1103/PhysRevA.76.042319.

tunable_param_names = ('E_C', 'E_J', 'n_g')

Parameters eligible for inverse design. DeviceModel derives these from declared fields unless the class or an ancestor supplies a tuple. Explicit tuples remain authoritative when inherited; an empty tuple excludes the device from inverse design. Plain BaseDevice subclasses default to an empty tuple without derivation.

approximation = 'Exact diagonalization in a finite integer-charge basis; accuracy is governed by num_basis.'

Declared approximation-regime statement surfaced by physics_notes() — the mechanism that keeps a model’s stated validity range attached to the class rather than buried in a docstring a caller may not read.

computational = True

Whether this device represents a computational qubit, as opposed to e.g. a bus resonator or a coupler element.

requires_projection_levels: ClassVar[bool] = True

structural_setting_names = ('num_basis', 'basis', 'projection_levels', 'collapse_model', 'coupling_channel', 'collapse_rate_threshold')

E_C: Scalar = Parameter(default=unbound, positive=True, nonnegative=False, serialize=True, unit='GHz', symbol='E_C', noise=False, kw_only=False, required=False)

E_J: Scalar = Parameter(default=unbound, positive=True, nonnegative=False, serialize=True, unit='GHz', symbol='E_J', noise=False, kw_only=False, required=False)

n_g: Scalar = Parameter(default=0.0, positive=False, nonnegative=False, serialize=True, unit=None, symbol='n_g', noise=False, kw_only=False, required=False)

dissipation(op, p)

Return device-local Lindblad channels.

Parameters:

• op (LocalOps) – Local operator namespace.

• p (ParameterNamespace) – Symbolic declared parameters.

• T1 (The base channels implement)

• T2

• Subclasses (and thermal occupation.)

• ``super().dissipation(op (may append channels with) –

• p)``.

local_space()

Return the authored integer-charge space.

local_hamiltonian(op, p)

Return the charge-basis transmon Hamiltonian.

Parameters:

• op (LocalOps) – Charge-space operator namespace.

• p (ParameterNamespace) – Symbolic E_C, E_J and n_g values.

property freq: Any

Return the isolated 0-to-1 transition in GHz.

eigenenergies()

Return isolated energies shifted to zero at the ground state.

eigenvectors()

Return the isolated energy-ordered eigenvectors in the charge basis.

charge_coupling_operator()

Return the authored charge operator.

phase_coupling_operator()

Return sin(phi) in the authored charge basis.

tunable_param_bounds(name, value)

Return physical bounds for a tunable parameter.

Parameters:

• name (str) – Tunable parameter name.

• value (float) – Concrete optimizer seed.

physics_notes()

Return base device notes plus the declared approximation, if any.

classmethod from_frequency(freq, anharmonicity, n_g=0.0, levels=None, label=None, *, num_basis=61, basis=None, **kwargs)

Construct from the leading transmon-regime inversion.

Parameters:

• freq (float) – Calibrated transition and anharmonicity in GHz.

• anharmonicity (float) – Calibrated transition and anharmonicity in GHz.

• n_g (float, default 0.0) – Offset charge in Cooper-pair units.

• levels (int or None, default None) – Projected eigenstate count.

• label (str or None, default None) – Device label.

• num_basis (int, keyword-only, default 61) – Odd charge-basis dimension.

• basis ({None, "native", "eigen"}, keyword-only) – Basis policy.

• **kwargs (Any) – Noise and other constructor keyword arguments.

to_dict()

Serialize common device state and declared parameter values.

classmethod from_dict(data)

Reconstruct from serialized constructor data.

Parameters:

data (mapping) – Record produced by to_dict().