quchip.control.drives_two_photon

TwoPhotonDrive – parametric two-photon drive for Kerr-cat qubits.

Physical Hamiltonian (lab frame):

H_drive = eps2(t) * [a_dag^2 * exp(-i*2pi*omega_d*t) + a^2 * exp(+i*2pi*omega_d*t)]

At resonance (omega_d = 2*omega_f), the rotating-frame Hamiltonian is:

H_rot = eps2(t) * (a_dag^2 + a^2)

The coupling operator is a^2 + a_dag^2 and the drive is assembled by the engine’s DriveModulation.SINGLE_TONE dispatch – the same carrier-mixing path used for charge and phase drives. Setting the carrier frequency to 2*omega_f ensures that each operator band picks up the correct two-photon detuning.

SINGLE_TONE’s real-field projection halves the scheduled amplitude: an envelope of amplitude A(t) scheduled on this drive contributes A(t)/2 * (a_dag^2 + a^2) to H_rot, not A(t) * (a_dag^2 + a^2). Scheduling amplitude = 2*eps2(t) realizes the eps2(t) coefficient shown in H_rot above.

References

Classes

TwoPhotonDrive([target, label, rwa])

Parametric two-photon drive for Kerr-cat qubit stabilisation.
class quchip.control.drives_two_photon.TwoPhotonDrive(target=None, *, label=None, rwa=None)[source]

Bases: BaseDrive

Parametric two-photon drive for Kerr-cat qubit stabilisation.

Coupling operator: a^2 + a_dag^2

The drive should be scheduled at twice the cavity frequency (freq = 2 * cavity.freq) so that in the rotating frame the interaction is static: eps2(t) * (a_dag^2 + a^2). This combination of Kerr nonlinearity and two-photon drive creates and stabilises cat states.

Uses the standard DriveModulation.SINGLE_TONE carrier dispatch – no engine modifications required. The engine band-decomposes a^2 + a_dag^2 into bands of excitation weight Delta_n = +2 and Delta_n = -2, attaching the correct two-photon carrier automatically.

SINGLE_TONE’s real-field projection contributes only half the scheduled envelope amplitude to each band: the coefficient landing on a_dag^2 + a^2 in the rotating frame is A(t)/2, where A(t) is the amplitude scheduled on this drive’s envelope. Schedule amplitude=2*eps2(t) to realize the target two-photon drive strength eps2(t) used above and in alpha^2 = eps2/K.

Parameters:

  • target (BaseDevice | None) – Device to connect this drive to. None means unconnected.

  • label (str | None) – Optional explicit label; otherwise auto-generated.

  • rwa (bool | None) – Per-drive RWA override. None means follow the chip-level setting.

References

Examples

>>> from quchip.devices.kerr_cavity import KerrCavity
>>> from quchip.control.drives_two_photon import TwoPhotonDrive
>>> cav = KerrCavity(freq=5.0, kerr=1.0, levels=10, label="cav")
>>> d2 = TwoPhotonDrive(target=cav)
>>> channels = d2.local_channels(cav)
>>> len(channels)
1
local_channels(device)[source]

Return the two-photon coupling channel a^2 + a_dag^2.

Parameters:

device (BaseDevice) – The cavity device being driven.

Returns:

One channel with operator a^2 + a_dag^2 and DriveModulation.SINGLE_TONE modulation.

Return type:

list[DriveChannel]

physics_notes()[source]

Return the base drive notes plus the two-photon coupling declaration.

Return type:

list[str]