Auxiliary Quantum System for Tunable Coupler Interaction Control
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Solution Overview
Problem
In superconducting quantum architectures, tunable couplers face challenges such as spurious cross-Kerr or ZZ coupling even when in the 'off' position, leading to undesired interactions and qubit errors due to noise sensitivity in control parameters, which limits the on-off ratio and increases cross-talk errors.
Innovation Solution
The introduction of an auxiliary quantum system with an attenuation drive generates stabilized states that become entangled with the coupler's eigenstates, reducing the probability of undesired interactions by controlling the transition probability exponentially with the attenuation drive amplitude, thereby enhancing the coupler's on-off ratio and reducing noise sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a tunable coupler is used to enable on-demand quantum interactions, then interaction control capability is improved, but spurious cross-Kerr or ZZ coupling occurs when the coupler is in the 'off' position, leading to undesired interactions
Solution Approach 1:
The patent introduces an auxiliary quantum subsystem as an intermediary between the first and second quantum subsystems. This auxiliary subsystem mediates the interaction by becoming entangled with the coupler's eigenstates, thereby suppressing spurious direct couplings between the main quantum subsystems while maintaining controlled interaction capability.
Solution Approach 2:
The patent employs an attenuation drive that modifies the coupling parameters dynamically. By adjusting the attenuation drive amplitude, the system changes the effective coupling strength between quantum subsystems, enabling exponential suppression of spurious interactions when needed while maintaining strong coupling when desired.
2Speed
If the coupler is made tunable to achieve fast switching between on and off states, then switching speed is improved, but noise in the control parameter limits the on-off ratio and introduces qubit errors
Solution Approach 1:
The auxiliary quantum subsystem acts as a mediator that decouples the direct sensitivity to control noise. By routing interactions through the auxiliary subsystem and entangling it with the coupler's eigenstates, the system reduces the direct impact of control parameter noise on the main quantum subsystems, thereby improving reliability.
Solution Approach 2:
The attenuation drive applies a preliminary suppressive action on the coupler's transition probability before noise can significantly affect the system. By pre-establishing the entanglement between the auxiliary subsystem and coupler eigenstates, the system proactively reduces the probability of undesired transitions, counteracting the effects of control noise.
3Object-generated harmful factors
If the coupler is kept in the 'off' position to prevent undesired interactions, then cross-talk errors are reduced, but the auxiliary quantum subsystem and attenuation drive are required, increasing device complexity
Solution Approach 1:
The auxiliary quantum subsystem serves multiple functions: it mediates controlled interactions between quantum subsystems, suppresses spurious couplings when the coupler is off, and provides a mechanism for exponential attenuation of undesired interactions. This multi-functionality justifies the added complexity by consolidating several protective and control roles into a single subsystem.
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 approach effectively suppresses spurious interactions and qubit errors by exponentially reducing the transition probability of the coupler's eigenstates, improving the coupler's on-off ratio and reducing noise sensitivity, thus enhancing the control over quantum interactions and maintaining coherence.
Implementation Method 1
the stabilized states become entangled with the eigenstates
Implementation Method 2
generate a quantum interaction such as entanglement or disentanglement between the eigenstates of the coupled quantum subsystems
Implementation Method 3
an example detailed further below presents a cross-Kerr in situ interaction which, although not technically being a longitudinal interaction, exhibits longitudinal interaction dynamics
Data Source
AI summary
The generally quantum system can have : a first quantum subsystem having a first set of eigenstates; a second quantum subsystem having a second set of eigenstates; a coupler connected to both the first quantum system and to the second quantum system, the coupler having a third set of eigenstates; at least one interaction drive configured to control interaction between the first set of eigenstates and the second set of eigenstates via transitions within the third set of eigenstates; an auxiliary quantum subsystem connected to the coupler; and an attenuation drive selectively operable at a drive amplitude to generate a set of stabilized states in the auxiliary quantum system, said set of stabilized states being entangled with the third set of eigenstates in a manner that the probability of said transition within the third set of eigenstates is set by a probability of transition in the set of stabilized states.