Quantum Bit Conversion Achieved with Hybrid-Entangled State
Researchers at the Kastler Brossel Laboratory in Paris have achieved a breakthrough in the field of quantum computing by creating the first converter between two different types of quantum-bit encodings. This high-quality conversion of information is a step towards bringing together the many different platforms competing in the race for quantum computing and connecting future quantum networks.
In the February issue of Nature Photonics, a team of researchers led by Professor Julien Laurat at the Kastler Brossel Laboratory reported the successful demonstration of faithful qubit-encoding conversion. The quantum realm has two distinct ways of storing and processing information, called discrete and continuous variables.
Like classical information encodings, these two types of quantum information are suitable for different tasks and platforms. The researchers at the Kastler Brossel Laboratory have found a way to convert between these two distinct flavors of quantum information, demonstrating the potential for interconnecting different quantum devices.
In the pursuit of quantum computing, various platforms are being developed, using different quantum systems such as photons, neutral atoms, ions, superconductors, and semiconductors. Each of these systems has multiple types of encodings, and the choice of encoding depends on the specific application and available resources. The challenge of addressing this heterogeneity in quantum networks is a pressing issue, as it would allow for the integration of the best features of each system, resulting in more robust and efficient networks.
Addressing the issue of heterogeneity in quantum networks early on can prevent compatibility problems and enable smooth integration and interconnectivity between different quantum systems in the future. This requires the use of a quantum encoding converter, a device that can change the basis of the encoded quantum information signal while preserving its integrity.
Converting quantum bits is a difficult challenge. The simplest way to create a converter would be to measure the information stored in one encoding and recreate it in the other encoding, but this is not possible due to the laws of quantum mechanics and the so-called no-cloning theorem.
Although this restriction is a challenge, it is also the source of the power of quantum cryptography. The team at the Kastler Brossel Laboratory had to take a different approach to create a converter and used quantum entanglement instead.
Addressing the issue of heterogeneity in quantum networks early on can help prevent compatibility problems and facilitate seamless integration and interconnectivity between different quantum systems in the future. This requires the use of a quantum encoding converter, a device that can change the encoding of the quantum information signal while preserving its delicate nature.
The task of converting quantum bits is complex. The most straightforward method would be to measure the information stored in one encoding and recreate it in the other encoding, but this is not possible due to the laws of quantum mechanics and the no-cloning theorem.
While this limitation presents a challenge, it also serves as the foundation of quantum cryptography. The researchers at the Kastler Brossel Laboratory had to find another way to create a converter and used quantum entanglement as a solution.
The researchers at Kastler Brossel Laboratory in Paris used high-quality nonlinear optical sources, known as optical parametric oscillators, and superconducting single-photon detectors to generate the resource states necessary for the conversion process.
The creation of the converter required a specific type of optical entanglement, known as a “hybrid-entangled state,” between a discrete-variable qubit and a continuous-variable Schrödinger cat qubit.
To enable a Bell-state measurement, the single-photon part of the hybrid entanglement was made to interfere with the input qubit, followed by a boosted single-photon detection. The output qubit was then characterized using quantum tomography to calculate the fidelity between the input and output qubits.
The successful demonstration of the conversion process is considered an important milestone for quantum technology, as it opens up the possibility for the creation of more complex and efficient quantum networks.
According to Beate Asenbeck, a Ph.D. student at LKB and one of the lead authors of the study, the success of this process is remarkable given that with technology from just ten years ago, this task would have been nearly impossible. The advancement of our fundamental understanding of the quantum realm is pushing the boundaries of technology, making it an exciting time for the field.
More information: Tom Darras et al, A quantum-bit encoding converter, Nature Photonics (2022). DOI: 10.1038/s41566-022-01117-5