Researchers from the Korea Advanced Institute of Science and Technology, Jiheon Seong and Joonwoo Bae, have developed an entanglement witness circuit to detect quantum entanglement of qubits in cloud-based quantum computing services. Their research aims to address the challenge of detecting entanglement when users have limited control over the quantum machine.

Entanglement is crucial for achieving quantum advantages in computing. A quantum machine can accelerate certain calculations if two or more qubits exhibit correlated behavior, even when separated. Researchers want to build circuits that generate entanglement between qubits, but they need a way to certify whether a circuit does or does not generate entanglement.

One approach is quantum tomography, a costly procedure that researchers can use to determine if a circuit generates entanglement. However, this method is not practical in all scenarios. Another option is to use an entanglement witness, which is a mathematical function that relates specific qubits and their states. The output of the entanglement witness indicates whether the qubits’ states are entangled or separable.

The challenge arises when researchers do not have direct access to the quantum machine in cloud-based services. In such cases, the allocation of hardware qubits to a circuit is controlled by the service, and the researcher cannot be certain of obtaining the required values to calculate the output of the entanglement witness function.

To overcome this limitation, Seong and Bae developed entanglement witness circuits that utilize the entanglement witness strategy to certify the presence of entangled qubits. These circuits allow researchers to detect entanglement using only the measurement statistics provided by the cloud-based service, without the need to control qubit allocation. This enables researchers to fulfill the essential requirement of seeking quantum advantages in cloud-based quantum computing.

The newly developed entanglement witness circuits are based on the EW 2.0 framework, which is twice as efficient in detecting entanglement. The researchers described the entanglement detection in circuits that generate entanglement of two and three qubits and outlined two approaches to constructing entanglement witness circuits. They also shared the results of experiments conducted using IBMQ and IonQ’s cloud-based quantum computing services.

In conclusion, Seong and Bae’s work provides a solution for detecting entanglement in cloud-based quantum computing services, where users have limited control over the quantum machine. By using entanglement witness circuits, researchers can certify the presence of entangled qubits and explore the potential for quantum advantages in computing.

Source:
– Publication: Intelligent Computing (2023)
– DOI: 10.34133/icomputing.0051