Ingrid Fadelli is a writer for the website Phys.org.
When two particles are entangled, they stay connected even when separated. This phenomenon is important for both the development of quantum technology and the study of quantum physics.
Researchers at Tsinghua studied the possible reasons why the reliable and efficient detection of entanglement in complex and noisy systems has often proved to be very difficult. There is a trade-off between the effectiveness and efficiency of detection methods.
One of the researchers who carried out the study said that most quantum states are entangled.
If we were to build a 100qubit quantum computing system, it would evolve for a while, during which the qubits interact with each other. The system should be isolated from the environment to maintain a good control. The system is likely to be entangled if the purity is not small and the number of qubits is large.
It's not easy to achieve entanglement in experimental settings. It is difficult in large quantum systems. Ma and his colleagues wanted to gain a better understanding of the challenges associated with the detection of large systems.
Researchers realized that the preparation of entangled state for a large system could be very challenging. We created a mathematical formula to measure the effectiveness of anentanglement detection method. We use a proper quantum state distribution, use the ratio of entangled state to measure effectiveness, and use the number of observables needed for this method.
Ma and his colleagues looked at what is arguably the most straightforward protocol available today. As the system grows, the protocol's ability to detect entanglement decreases.
The researchers found that the size of the system had an effect on other protocols. They were able to extend their observations of the entanglement witnesses method's performance to arbitrary entangled protocols that rely on single-copy quantum state measurement.
Ma said that single-copy realization is either inefficient or ineffective for a random state. The effectiveness of the protocol depends on measuring an exponential number of observables.
Researchers must be able to control all interactions in a system with high precision and know almost all information about them if they want to observe entanglement on a large-scale. If there is a lot of uncertainty about the system, the chances of detecting it are very small.
No entanglement detection protocols are both efficient and effective. The design of entanglement detection protocols could be improved by this. It's a good indicator for comparing different quantum computing systems. When a lab team claims to have built a hundreds-of-qubit system, they should look for it. They didn't control the system enough.
The findings of this team of researchers show that there is a trade-off between the efficiency and effectiveness of existing methods. They offer valuable insight about the reasons why it's difficult to detectentanglement in large-scale and noisy quantum systems.
We can still design a protocol that is both efficient and effective when the system is well-controlled. We only have protocols that work for pure states, such as entanglement witnesses, and protocols that work for large environments at the expense of cost. We would like to try to develop a protocol that works for moderate environment size with relatively low cost.
There is more information about the fundamental limitation on the detection ofanglement. There is a book titled "PhysRevLett.129.230503."
The volume of the set of separable states was published. There is a DOI titled "10103/PhysRevA.58.883".
The largest separable balls are around the quantum state. There is a DOI titled "10.103/PhysRevA. 66.062311".
The volume of separable states is very small in the number of qubits. There is a book titled "PhysRevA.72.032304."
The 18-Qubitanglement with Six Photons' Three Degrees of Freedom was published. There is a book titled "PhysRevLett."
Journal information: Physical Review Letters , Physical Review A
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