Device-independent method certifies genuinely entangled subspaces in photonic and superconducting systems

In a study published in Relations on progress in physicsThe researchers have reached the independent characterization of the apparatus of truly tangled subspaces (GESS) in the optical and superconducting quantum systems, supplementing the self-truth of the error correction code space of five qubit.

In quantum information, truly multi-party tangled states require the existence of correlations of entanglement between two system subsystems. The GE constituted by states has an application value, in particular in the design of quantum errors correction codes. By coding for quantum information in the subspace, it can prevent the propagation of errors caused by local decoherence.

Scientists have built a new bell inequality based on the stabilizer code frame built, and the tangled subspace can be universally characterized by using it. Any quantum state (including mixed states) in this subspace could violate this inequality as much as possible, providing a theoretical basis for the auto-test of real tangled subspaces.

In this study, to verify inequalities, the researchers conducted two proof experiences in principle implementing the code to five qubit using photonic and superconductive platforms. They obtained independent certification from the device of the quantum error correction space at five BBITS.

During the verification process, the researchers prepared a series of logical quantum states and carried out bell tests. They found that the logical underemployment of the two systems reached more than 82% and 62% respectively. This process was based solely on the data observed in the experience without requiring reliable hypotheses on experimental equipment.

For experiences on photonic and superconducting platforms, the researchers simulated a single scenario of physical bit error and found that the logical state has completely lost its ability to violate the inequality of the bell, demonstrating that it had deviated from the target logical subspace.

By further checking the inequality of the bells corresponding to the error subspaces, the researchers have managed to monitor the evolution of the logical quantum state space.

The study demonstrates the feasibility of the independent certification of the apparatus of general quantum structures entangled in experimental contexts, extending beyond quantum and quantum states. The research teams were led by Guo Guangcan and Professor Liu Biheng of the University of Science and Technology of China (USTC) of the Chinese Academy of Sciences, in collaboration with Origin Quantum Computing Company Limited.