中奥科学家合作首次实现了复杂量子隐形传态

诸平

中国科学家和奥地利科学家首次成功地转移了三维量子态。在未来的量子计算机中，高维隐形传态将发挥重要作用。来自奥地利科学院和维也纳大学的研究人员，与中国科学技术大学的量子物理学家一起，他们成功地实现了复杂高维量子态的远程传输。相关研究结果于2019年8月15日在《物理评论快报》（Physical Review Letters）杂志发表——Yi-Han Luo, Han-Sen Zhong, Manuel Erhard, Xi-Lin Wang, Li-Chao Peng, Mario Krenn, Xiao Jiang, Li Li, Nai-Le Liu, Chao-Yang Lu, Anton Zeilinger, and Jian-Wei Pan. Quantum Teleportation in High Dimensions. Phys. Rev. Lett., 2019, 123, 070505. DOI: 10.1103/PhysRevLett.123.070505 – Published 15 August 2019.更多信息请注意浏览原文或者相关报道。

Complex quantum teleportation achieved for the first time

by University of Vienna

Austrian and Chinese scientists have for the first time succeeded in transferring three-dimensional quantum states (symbolic image). Credit: ÖAW/Harald Ritsch

Austrian and Chinese scientists have succeeded in teleporting three-dimensional quantum states for the first time. High-dimensional teleportation could play an important role in future quantum computers.

Researchers from the Austrian Academy of Sciences and the University of Vienna have experimentally demonstrated what was previously only a theoretical possibility. Together with quantum physicists from the University of Science and Technology of China, they have succeeded in teleporting complex high-dimensional quantum states. The research teams report this international first in the journal Physical Review Letters.

In their study, the researchers teleported the quantum state of one photon (light particle) to another distant one. Previously, only two-level states ("qubits") had been transmitted, i.e., information with values "0" or "1". However, the scientists succeeded in teleporting a three-level state, a so-called "qutrit". In quantum physics, unlike in classical computer science, "0" and "1" are not an 'either/or' – both simultaneously, or anything in between, is also possible. The Austrian-Chinese team has now demonstrated this in practice with a third possibility "2".

Novel experimental method

It has been known since the 1990s that multidimensional quantum teleportation is theoretically possible. However: "First, we had to design an experimental method for implementing high-dimensional teleportation, as well as to develop the necessary technology", says Manuel Erhard from the Vienna Institute for Quantum Optics and Quantum Information of the Austrian Academy of Sciences.

The quantum state to be teleported is encoded in the possible paths a photon can take. One can picture these paths as three optical fibers. Most interestingly, in quantum physics a single photon can also be located in all three optical fibers at the same time. To teleport this three-dimensional quantum state, the researchers used a new experimental method. The core of quantum teleportation is the so-called Bell measurement. It is based on a multiport beam splitter, which directs photons through several inputs and outputs and connects all optical fibers together. In addition, the scientists used auxiliary photons—these are also sent into the multiple beam splitter and can interfere with the other photons.

Through clever selection of certain interference patterns, the quantum information can be transferred to another photon far from the input photon, without the two ever physically interacting. The experimental concept is not limited to three dimensions, but can in principle be extended to any number of dimensions, as Erhard emphasizes.

Higher information capacities for quantum computers

With this, the international research team has also made an important step towards practical applications such as a future quantum internet, since high-dimensional quantum systems can transport larger amounts of information than qubits. "This result could help to connect quantum computers with information capacities beyond qubits", says Anton Zeilinger, quantum physicist at the Austrian Academy of Sciences and the University of Vienna, about the innovative potential of the new method.

The participating Chinese researchers also see great opportunities in multidimensional quantum teleportation. "The basics for the next-generation quantum network systems is built on our foundational research today", says Jian-Wei Pan from the University of Science and Technology of China. Pan recently held a lecture in Vienna at the invitation of the University of Vienna and the Academy.

In future work, the quantum physicists will focus on how to extend the newly gained knowledge to enable teleportation of the entire quantum state of a single photon or atom.

ABSTRACT

Quantum teleportation allows a “disembodied” transmission of unknown quantum states between distant quantum systems. Yet, all teleportation experiments to date were limited to a two-dimensional subspace of quantized multiple levels of the quantum systems. Here, we propose a scheme for teleportation of arbitrarily high-dimensional photonic quantum states and demonstrate an example of teleporting a qutrit. Measurements over a complete set of 12 qutrit states in mutually unbiased bases yield a teleportation fidelity of 0.75(1), which is well above both the optimal single-copy qutrit state-estimation limit of $1/2$ and maximal qubit-qutrit overlap of $2/3$, thus confirming a genuine and nonclassical three-dimensional teleportation. Our work will enable advanced quantum technologies in high dimensions, since teleportation plays a central role in quantum repeaters and quantum networks.