Probing coherent and relaxation times at different frequencies¶
Often superconducting qubits are operated at their “sweetspot”, i.e. the point where the external noise is reduced. In the case of flux-tunable qubits this points corresponding to the maximum frequency achievable by the qubit as discussed in Frequency vs flux experiments.
Even if the sweetspot should be the ideal point in order to achieve high relaxation time \(T_1\) and coherence time \(T_2\), it is not always the case due to the presence of individual Two Level System (TLS) [12].
For this reason it is interesting to evaluate both the relaxation time and the coherence time while operating the qubit at different frequencies. A possible way to measure them [12] is to change the static bias of the qubit and recalibrate the qubit in the new operative point as shown in [18]. To avoid recalibrating the qubit at each frequency, a clever approach consists in dynamically changing the frequency of the qubit using fast flux pulses. In fact, in both the \(T_1\) and the \(T_2\) if we play a flux pulse during the idling time of the qubit we can effectively probe both the relaxation and the coherence time of the qubit at different frequencies without the need of recalibrating the qubit.
T1 outside the sweetspot¶
In this experiment we sweep different values of qubit frequency by applying a flux pulse with variable amplitude. For each of these values we individually measure the relaxation time \(T_1\) of the qubit.
Parameters¶
- class qibocal.protocols.coherence.t1_flux.T1FluxParameters(delay_min: int, delay_max: int, delay_step: int, amplitude_min: float, amplitude_max: float, amplitude_step: float)[source]
T1 runcard inputs.
- delay_min: int
Initial delay before readout [ns].
- delay_max: int
Final delay before readout [ns].
- delay_step: int
Step delay before readout [ns].
- amplitude_min: float
Flux pulse minimum amplitude.
- amplitude_max: float
Flux pulse maximum amplitude.
- amplitude_step: float
Flux pulse amplitude step.
- property delay_range: ndarray[tuple[Any, ...], dtype[_ScalarT]]
Return the delay range as a numpy array.
- property flux_range: ndarray[tuple[Any, ...], dtype[_ScalarT]]
Return the flux pulse amplitude range as a numpy array.
- hardware_average: bool = False
By default hardware average will be performed.
- nshots: int
Number of executions on hardware.
- relaxation_time: float
Wait time for the qubit to decohere back to the gnd state.
Example¶
- id: t1 study
operation: t1_flux
parameters:
delay_max: 10000
delay_min: 4
delay_step: 100
amplitude_min: 0
amplitude_max: 0.1
amplitude_step: 0.02
nshots: 1000
A possible outcome measured on a qubit is the following
Requirements¶
T2 outside the sweetspot¶
In this experiment we sweep different values of qubit frequency by applying a flux pulse with variable amplitude. For each of these values we individually measure the relaxation time \(T_2\) of the qubit.
Parameters¶
- class qibocal.protocols.coherence.t2_flux.T2FluxParameters(delay_min: int, delay_max: int, delay_step: int, amplitude_min: float, amplitude_max: float, amplitude_step: float)[source]
T2 flux runcard inputs.
- property delay_range: ndarray[tuple[Any, ...], dtype[_ScalarT]]
Return the delay range as a numpy array.
- property flux_range: ndarray[tuple[Any, ...], dtype[_ScalarT]]
Return the flux pulse amplitude range as a numpy array.
- hardware_average: bool = False
By default hardware average will be performed.
- delay_min: int
Initial delay before readout [ns].
- delay_max: int
Final delay before readout [ns].
- delay_step: int
Step delay before readout [ns].
- amplitude_min: float
Flux pulse minimum amplitude.
- amplitude_max: float
Flux pulse maximum amplitude.
- amplitude_step: float
Flux pulse amplitude step.
- nshots: int
Number of executions on hardware.
- relaxation_time: float
Wait time for the qubit to decohere back to the gnd state.
Example¶
- id: t2 study
operation: t2_flux
parameters:
delay_max: 10000
delay_min: 4
delay_step: 100
amplitude_min: 0
amplitude_max: 0.1
amplitude_step: 0.02
nshots: 1000
A possible outcome measured on a qubit is the following
