Quantum communication (QC) offers secure and future-proof tools for performing sensitive communication tasks. Quantum secure direct communication (QSDC) offers to protect the exchange of information between the distant partners Alice and Bob against any eavesdropping attempt. Established quantum key distribution (QKD) schemes achieve this by distributing quantum states of light, from which a shared secret key is distilled and used to encrypt a message. QSDC unifies these two steps by directly encoding a message into the exchanged quantum states. For the first time, Pan et al. experimentally demonstrate such a QSDC scheme implemented using phase-modulated single photon states sent over a free space optical link. With a security guarantee against collective and photon number splitting attacks in the asymptotic regime of many communication rounds, their system can in principle securely transmit up to 500 bits of text, picture, or audio files per second. While requiring a bidirectional state exchange in contrast to QKD, the authors' QSDC implementation needs no key management and denies eavesdroppers even the possibility to store and analyze encrypted ciphertexts. The paper thus adds an exciting new tool to the growing QC toolbox, shaping the communication infrastructures of the future.
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