Qubit Leakage Removal Using a Damped Cavity Mode
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Solution Overview
Problem
Quantum bits (qubits) experience parasitic occupation of higher levels, known as leakage, which hampers quantum computation due to inaccurate readout and slow decay, leading to significant occupation outside the computational subspace, especially in qubits with weak non-linearity.
Innovation Solution
A damped cavity mode is used to transfer and damp parasitic occupation of higher qubit levels without prior knowledge of the qubit state, by adjusting the qubit frequency to align or sweep past the cavity frequency, allowing population transfer and damping of non-computational levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If qubit frequency is adjusted to align with cavity frequency for population transfer, then leakage removal effectiveness is improved, but system complexity increases due to frequency control requirements
Solution Approach 1:
The qubit frequency is dynamically adjusted to align with the cavity frequency during the leakage removal process. The frequency controller modifies the qubit frequency in real-time to match the cavity frequency, enabling resonant population transfer from computational to non-computational levels, which is then damped through the cavity.
Solution Approach 2:
The system employs a frequency controller that monitors and adjusts the qubit frequency based on the cavity frequency. This feedback mechanism ensures that the qubit frequency is continuously optimized to maintain alignment with the cavity, maximizing the population transfer efficiency while managing the control complexity.
2Productivity
If damped cavity mode is used to transfer parasitic occupation, then leakage removal speed is improved, but hardware overhead increases due to additional cavity and couplers
Solution Approach 1:
A damped cavity is introduced as an intermediary system between the qubit and the environment. The cavity acts as a mediator that facilitates the transfer of population from computational qubit levels to non-computational levels through resonant coupling, and then dissipates this population through controlled damping, thereby accelerating leakage removal.
Solution Approach 2:
The damped cavity serves multiple functions: it provides a resonant coupling mechanism for population transfer, acts as a temporary storage for parasitic occupation, and functions as a damping channel to dissipate the leaked population. This multi-functionality justifies the additional hardware by consolidating several leakage removal mechanisms into a single system.
3Ease of operation
If frequency sweeping is performed to transfer population, then prior knowledge of qubit state becomes unnecessary, but control precision requirements increase
Solution Approach 1:
The frequency controller performs periodic frequency sweeping of the qubit, cycling through a range of frequencies that includes the cavity frequency. This periodic action ensures that regardless of the initial qubit state, the system will eventually pass through the resonant condition, enabling population transfer without requiring prior knowledge of the qubit's computational or non-computational level occupation.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This method effectively reduces higher level occupations in qubits, improving computational efficiency and robustness by enabling quick leakage removal with minimal hardware overhead and no need for prior state knowledge, thus enhancing quantum computation performance.
Implementation Method 1
The parasitic occupation may be damped in the cavity using the damped cavity mode
Implementation Method 2
By moving the quantum bit in frequency close to the damped cavity frequency, parasitic occupation of higher levels will transfer to the cavity
Data Source
AI summary
Apparatus and methods for removing leakage from a qubit. In one aspect, an apparatus includes one or more qubits, wherein each qubit facilitates occupation of at least one of a plurality of qubit levels, the qubit levels including two computational levels and one or more non-computational levels that are each higher than the computational levels, wherein the qubit facilitates transitions between qubit levels associated with a corresponding transition frequency; a cavity, wherein the cavity defines a cavity frequency; one or more couplers coupling each qubit to the cavity; one or more couplers coupling the cavity to an environment external to the one or more qubits and the cavity; a frequency controller that controls the frequency of each qubit such that, for each qubit, the frequency of the qubit is adjusted relative to the cavity frequency such that a population of a non-computational level is transferred to the cavity.