Stationary Quantum State Preparation Through Iterative Low-Depth Evolution
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Solution Overview
Problem
Existing quantum computing methods for constructing stationary quantum states, such as ground or excited states, require variational minimization and result in high computational resource consumption and error accumulation, making them unsuitable for near-term quantum devices with noise issues.
Innovation Solution
An iterative process for constructing quantum circuits that evolve an initial quantum state using computed parameter values and evolution times, approximating time evolution with low rank decompositions and unitary compression, reducing circuit depth and improving accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If variational minimization is used to construct stationary quantum states, then the quantum states can be prepared, but computational resource consumption increases and error accumulation occurs
Solution Approach 1:
The patent segments the complex variational minimization process into simpler iterative steps involving quantum circuit evolution. Instead of performing full variational minimization, the method divides the process into discrete iterations where quantum circuits evolve states using computed parameter values and evolution times, reducing computational complexity at each step while maintaining overall accuracy.
Solution Approach 2:
The patent applies preliminary action by pre-computing parameter values and evolution times before executing the quantum circuit evolution. This allows the quantum device to directly evolve states without performing minimization during execution, reducing runtime computational resources and error accumulation while still achieving accurate stationary quantum state preparation.
2Reliability
If variational minimization is used to construct stationary quantum states, then the quantum states can be prepared, but error accumulation increases making them unsuitable for near-term quantum devices
Solution Approach 1:
The patent extracts and removes the variational minimization step from the quantum circuit execution process. By separating the parameter computation (done classically or with minimal quantum resources) from the state evolution (done on the quantum device), the method eliminates the source of error accumulation associated with iterative minimization on noisy quantum hardware, making the approach suitable for near-term devices.
Solution Approach 2:
The patent uses disposable, low-cost quantum circuit evolutions instead of expensive, error-prone variational minimization iterations. Each quantum circuit evolution is a simple, shallow operation that can be executed with minimal resources and low error rates, and multiple such evolutions can be performed without accumulating significant errors, unlike deep variational minimization circuits.
3Measurement precision
If complex quantum circuits are used for state evolution, then accurate stationary states can be prepared, but circuit depth increases leading to more errors
Solution Approach 1:
The patent introduces dynamics by using time-dependent evolution parameters and adaptive circuit depth adjustment. The quantum circuits evolve states with computed evolution times that optimize the balance between accuracy and circuit depth, allowing shallow circuits to achieve sufficient accuracy without requiring excessively deep circuits that would accumulate errors on noisy hardware.
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AI summary
Methods, systems and apparatus for preparing a target quantum state of a quantum system, where the target quantum state is stationary with respect to a parameterized many-body qubit operator. In one aspect a method includes preparing an initial quantum state as an input state for a first iteration; iteratively evolving the initial quantum state and subsequent input quantum states as inputs for subsequent iterations until an approximation of the target stationary quantum state is obtained, comprising, for each iteration: computing, by quantum computation, parameter values of the many-body qubit operator for the iteration; computing, by quantum computation, an evolution time for the iteration, comprising evaluating changes in elements of a 2-RDM for the iteration; and evolving the initial quantum state or the subsequent input quantum state for the iteration using the computed parameter values and evolution time to generate a subsequent input quantum state for the subsequent iteration.