Star Topology QPU Control Sequence for Digital-Analog Quantum Computation
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Solution Overview
Problem
Digital-analog quantum computation (DAQC) faces errors due to the on-off switching of multi-qubit interactions in stepwise DAQC, while banged DAQC mitigates these by keeping interactions constant, but introduces non-commutativity issues with single-qubit gates and the Hamiltonian, affecting qubit state evolution.
Innovation Solution
A method for determining a control sequence of analog blocks and single-qubit gates for a quantum processing unit with a star topology, where the sequence is optimized to simulate the target Hamiltonian by interleaving single-qubit gates with analog blocks, adjusting coupling coefficients, and applying gates before and after each block to align with the target Hamiltonian, thereby reducing errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If stepwise DAQC is used with on-off switching of multi-qubit interactions, then the qubit state evolution can be controlled, but errors arise from the switching process
Solution Approach 1:
The computation is divided into discrete time steps where multi-qubit interactions are turned on and off in controlled sequences. Each time step involves applying single-qubit gates followed by entangling operations, creating a segmented approach that enables precise control while managing errors through systematic timing.
Solution Approach 2:
Single-qubit gates are applied to qubits before the multi-qubit entangling operations begin. This preliminary action ensures that the qubits are in the correct initial state for the subsequent analog evolution, allowing for controlled state manipulation without introducing errors during the entangling process.
2Reliability
If banged DAQC is used with constant multi-qubit interactions, then switching errors are mitigated, but non-commutativity issues arise between single-qubit gates and the Hamiltonian
Solution Approach 1:
The system dynamically switches between different operational modes: during analog blocks, multi-qubit interactions are active while single-qubit gates are held idle; during digital gates, the interactions are frozen. This dynamic switching resolves the non-commutativity issue by ensuring that operations are applied in the correct temporal sequence, maintaining both accuracy and controllability.
Solution Approach 2:
The computation employs periodic alternation between analog evolution blocks and digital gate applications. This periodic structure allows the system to switch between continuous analog evolution and discrete gate operations, managing the complexity by creating a rhythmic pattern of operations that simplifies control while maintaining computational power.
3Productivity
If single-qubit gates are applied simultaneously with analog blocks in banged DAQC, then the computation can proceed continuously, but the evolution deviates from the idealized stepwise model
Solution Approach 1:
The continuous computation is segmented into distinct analog blocks and digital gate periods. Within each analog block, only multi-qubit interactions occur while single-qubit gates are held idle. This segmentation ensures that operations do not interfere with each other, maintaining fidelity by preventing simultaneous operations that would cause non-commutativity errors.
Data Source
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AI summary
The invention relates to the field of quantum computing. The invention includes a method for determining a control sequence for performing digital-analog quantum computation on a quantum processing unit with a star topology. The use of a QPU with this topology enables a significant reduction in the number of single qubit gates that must be applied to the system, thereby reducing circuit depth and reducing error. The invention also include a method for performing digital-analog quantum computation on a QPU with a star topology.