Ground-to-satellite quantum teleportation (1707.00934v1)

Abstract: An arbitrary unknown quantum state cannot be precisely measured or perfectly replicated. However, quantum teleportation allows faithful transfer of unknown quantum states from one object to another over long distance, without physical travelling of the object itself. Long-distance teleportation has been recognized as a fundamental element in protocols such as large-scale quantum networks and distributed quantum computation. However, the previous teleportation experiments between distant locations were limited to a distance on the order of 100 kilometers, due to photon loss in optical fibres or terrestrial free-space channels. An outstanding open challenge for a global-scale "quantum internet" is to significantly extend the range for teleportation. A promising solution to this problem is exploiting satellite platform and space-based link, which can conveniently connect two remote points on the Earth with greatly reduced channel loss because most of the photons' propagation path is in empty space. Here, we report the first quantum teleportation of independent single-photon qubits from a ground observatory to a low Earth orbit satellite - through an up-link channel - with a distance up to 1400 km. To optimize the link efficiency and overcome the atmospheric turbulence in the up-link, a series of techniques are developed, including a compact ultra-bright source of multi-photon entanglement, narrow beam divergence, high-bandwidth and high-accuracy acquiring, pointing, and tracking (APT). We demonstrate successful quantum teleportation for six input states in mutually unbiased bases with an average fidelity of 0.80+/-0.01, well above the classical limit. This work establishes the first ground-to-satellite up-link for faithful and ultra-long-distance quantum teleportation, an essential step toward global-scale quantum internet.

• The paper achieved quantum teleportation over 1400 km with an average fidelity of 0.80±0.01, marking a key experimental milestone.
• It employed advanced techniques including a compact ultra-bright photon source and a high-precision acquiring, pointing, and tracking system.
• The breakthrough reduces photon loss in quantum channels, paving the way for scalable global quantum communication networks.

An Exposition on Ground-to-Satellite Quantum Teleportation

The paper entitled "Ground-to-satellite quantum teleportation" presents a significant advancement in the field of quantum communication by successfully demonstrating quantum teleportation over an unprecedented distance of up to 1400 km from a ground observatory to a low Earth orbit satellite. This achievement addresses one of the pivotal challenges in the realization of a global quantum network: reducing channel loss over large distances. The experiment employs a satellite platform to bridge remote points on Earth via an up-link channel, thereby minimizing photon loss through the vacuum of space.

Methodological Advances

The researchers utilized several advanced techniques to optimize link efficiency and overcome atmospheric disturbances. A compact, ultra-bright source of multi-photon entanglement was developed, along with mechanisms for narrow beam divergence and high-accuracy acquiring, pointing, and tracking (APT). The teleportation process adhered to quantum principles, relying on the polarization of single photons as qubits. These qubits were generated at a ground station and beamed to the Micius satellite, which traverses a sun-synchronous orbit.

For quantum teleportation, both classical and quantum channels were employed. Experimental design included entangled photon pairs in the Bell state configuration. Central to the process was the execution of a Bell-state measurement (BSM), which effectively allowed one of the entangled photons to assume the state of the teleported photon. Despite the complexities, the experimental setup achieved an average fidelity of 0.80±0.01 for the teleported states, underscoring successful quantum state transfer unequivocally surpassing classical limits.

Experimental Setup

The groundwork for teleportation was established by integrating a high-intensity photon source configured to achieve multi-photon emissions. This was facilitated through the use of BiBO crystals, producing photons via spontaneous parametric down-conversion (SPDC). A notable aspect of the setup was the integration of a high-precision APT system to ensure effective photon transmission despite initial atmospheric turbulence in the uplink path.

In balancing photon visibility against environmental factors, the experiment mitigated challenges such as beam wandering through a dynamic optical arrangement. The quantum system was compact, maintaining a robust four-photon count rate, and utilizing a telescope with precise divergence measurements to crucially reduce channel attenuation.

Implications and Future Research

This work significantly furthers the potential implementation of a global-scale quantum internet by demonstrating ground-to-satellite quantum teleportation with minimized photon loss. Practically, the results suggest that quantum states can feasibly be shared over considerable terrestrial distances, paving the way for innovative applications in secure communication and distributed quantum computation.

Theoretically, the findings bolster the understanding and practical implementation of quantum entanglement over vast distances. Future endeavors might explore the distribution of entangled states over broader networks, seeking scalable entangled-photon sources capable of longer coherence times. Momentum could similarly shift towards the transfer of quantum states to/from quantum memories, enhancing protocols such as entanglement swapping.

The realization of spatially-distributed quantum computing elements and improvements in light-matter interfaces hint at the potential for crafting sophisticated space-scale quantum communication systems. Ultimately, the intersection of these technological advancements is expected to be a cornerstone in the burgeoning domain of the quantum internet.