Efficient Certification of Quantum States Using Few Single-Qubit Measurements

Keskeiset käsitteet

Almost all quantum states, including highly entangled ones, can be certified from only O(n^2) single-qubit measurements, where n is the number of qubits.

Tiivistelmä

The content presents a new technique for certifying the overlap between an n-qubit quantum state ρ synthesized in the lab and a target state |ψ⟩. The key idea is to define a "shadow overlap" ω that can be estimated using O(n^2) single-qubit Pauli measurements on ρ, and this shadow overlap provides a good surrogate for the fidelity ⟨ψ|ρ|ψ⟩.

The analysis establishes that for almost all n-qubit target states |ψ⟩, including highly entangled states with exponential circuit complexity, the relaxation time τ of a Markov chain related to the measurement distribution π(x) = |⟨x|ψ⟩|^2 is bounded by τ ≤ O(n^2). This allows the certification protocol to succeed with high probability using only O(n^2/ϵ) single-qubit measurements, where ϵ is the desired error tolerance.

The content also discusses several applications of the shadow overlap formalism, including:

1. Machine learning tomography of quantum states: The shadow overlap provides a theoretically backed yet practically feasible procedure for learning a machine learning model of a quantum state or certifying the fidelity of an already trained model.
2. Near-term benchmarking of quantum devices: The shadow overlap offers a flexible method for benchmarking noisy quantum devices, closely mirroring the fidelity.
3. Optimizing quantum circuits for state preparation: The shadow overlap exhibits favorable properties for training quantum circuits, avoiding the barren plateau phenomenon faced by fidelity-based training.

Tilastot

The content does not provide specific numerical data or statistics to support the claims. The focus is on the theoretical analysis and high-level applications of the shadow overlap certification procedure.

Lainaukset

There are no direct quotes from the content that are particularly striking or support the key logics.

Tärkeimmät oivallukset

Certifying almost all quantum states with few single-qubit measurements

by Hsin-Yuan Hu... klo arxiv.org 04-12-2024

https://arxiv.org/pdf/2404.07281.pdf

Syvällisempiä Kysymyksiä

How can the analysis of the relaxation time τ be extended to a broader class of quantum states beyond Haar-random states and the specific structured states considered?

The analysis of the relaxation time τ can be extended to a broader class of quantum states by exploring different families of states that exhibit specific properties. One approach is to investigate states that are efficiently preparable using random quantum circuits of varying depths and complexities. By studying the relaxation time of states prepared with random quantum circuits, we can determine if there is a general relationship between the circuit complexity and the relaxation time τ. This analysis can help identify classes of states that have a polynomial relaxation time, making them suitable for certification using the shadow overlap protocol. Additionally, exploring states that are close to Haar-random states in terms of their properties and entanglement structure can provide insights into the relaxation time of a wider range of quantum states.

Can the shadow overlap certification protocol be adapted to handle mixed quantum states, and what are the limitations in terms of the complexity of the mixed states that can be certified efficiently?

The shadow overlap certification protocol can be adapted to handle mixed quantum states by considering the overlap between a target mixed state and a prepared state. However, certifying mixed states efficiently poses challenges due to the increased complexity and entanglement present in such states. The limitations in certifying mixed states efficiently lie in the computational resources required to estimate the fidelity between the mixed state and the target state accurately. As the complexity of the mixed state increases, the sample complexity of the certification protocol may also increase, making it challenging to certify highly entangled mixed states with a polynomial number of single-qubit measurements. Therefore, while the shadow overlap protocol can be applied to mixed states, the efficiency of certification may be limited for complex mixed states with high entanglement.

Are there concrete examples of quantum states that cannot be certified using any protocol relying only on a polynomial number of single-qubit measurements?

There may be concrete examples of quantum states that cannot be certified using any protocol relying only on a polynomial number of single-qubit measurements. These states could potentially be highly entangled or have complex structures that require a more extensive measurement approach for accurate certification. For instance, states with intricate entanglement patterns or non-local correlations may pose challenges for certification with a limited number of single-qubit measurements. Additionally, states that exhibit specific properties or structures that are not easily captured by local measurements may also be difficult to certify efficiently using a protocol based solely on single-qubit measurements. In such cases, more sophisticated measurement techniques or additional resources may be necessary to certify these quantum states accurately.