Long-distance entanglement distribution is essential for both foundational tests of quantum physics and scalable quantum networks. Owing to channel loss, however, the previously achieved distance was limited to ~100 kilometers. Here we demonstrate satellite-based distribution of entangled photon pairs to two locations separated by 1203 kilometers on Earth, through two satellite-to-ground downlinks with a summed length varying from 1600 to 2400 kilometers. We observed a survival of two-photon entanglement and a violation of Bell inequality by 2.37 ± 0.09 under strict Einstein locality conditions. The obtained effective link efficiency is orders of magnitude higher than that of the direct bidirectional transmission of the two photons through telecommunication fibers.

Boson sampling is considered as a strong candidate to demonstrate the "quantum computational supremacy" over classical computers. However, previous proof-ofprinciple experiments suffered from small photon number and low sampling rates owing to the inefficiencies of the single-photon sources and multi-port optical interferometers. Here, we develop two central components for high-performance boson sampling: robust multi-photon interferometers with 99% transmission rate, and actively demultiplexed single-photon sources from a quantum-dot-micropillar with simultaneously high efficiency, purity and indistinguishability. We implement and validate 3-, 4-, and 5-photon boson sampling, and achieve sampling rates of 4.96 kHz, 151 Hz, and 4 Hz, respectively, which are over 24,000 times faster than the previous experiments. Our architecture is feasible to be scaled up to larger number of photons and with higher rate to race against classical computers, and might provide experimental evidence against the Extended Church-Turing Thesis.

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We report on entanglement-based quantum key distribution between a low-Earth-orbit satellite equipped with a space borne entangled-photon source and a ground observatory. One of the entangled photons is measured locally at the satellite, and the other one is sent via a down link to the receiver in the Delingha ground station. The link attenuation is measured to vary from 29 dB at 530 km to 36 dB at 1000 km. We observe that the two-photon entanglement survives after being distributed between the satellite and the ground, with a measured state fidelity of ≥0.86. We then perform the entanglement-based quantum key distribution protocol and obtain an average final key rate of 3.5  bits/s at the distance range of 530-1000 km.

Finding exponential separation between quantum and classical information tasks is like striking gold in quantum information research. Such an advantage is believed to hold for quantum computing but is proven for quantum communication complexity. Recently, a novel quantum resource called the quantum switch-which creates a coherent superposition of the causal order of events, known as quantum causality-has been harnessed theoretically in a new protocol providing provable exponential separation. We experimentally demonstrate such an advantage by realizing a superposition of communication directions for a two-party distributed computation. Our photonic demonstration employs d-dimensional quantum systems, qudits, up to d = 2 13 dimensions and demonstrates a communication complexity advantage, requiring less than (0.696 ± 0.006) times the communication of any causally ordered protocol. These results elucidate the crucial role of the coherence of communication direction in achieving the exponential separation for the one-way processing task, and open a new path for experimentally exploring the fundamentals and applications of advanced features of indefinite causal structures.Computation by separated parties with minimal communication is the focus of communication complexity, which has applications to distributed computing, very-large-scale integration, streaming algorithms, and more [1]. For quantum information, communication complexity is especially exciting as exponential quantum-classical gaps can be proven [2][3][4][5][6][7][8][9]. By contrast, exponential quantum-classical gaps for computation tasks such as factorization [10] depend on the best-known classical algorithm, and thus are strongly believed but not rigorously proven. Experimentally, quantum communication complexity has been studied in proof of principle for the quantum fingerprinting protocol [11][12][13] and beyond [1,14,15].The quantum switch provides a new communication complexity tool that leads to another instance of exponential quantum advantage [16]. The quantum switch is a device where a control qubit determines the order in which two transformations are performed on a target system [17,18]. When the control is in a superposition of logical states, the order of the operations is causally indefinite; i.e., there is a superposition of the ordering of target operations. The quantum switch has broad relevance in the context of quantum causality [19] including applications to studies of quantum gravity [19][20][21][22], communication complexity [16, * These authors contributed equally to this work.2 23], witnessing causality [17,[24][25][26][27][28] and deciding whether a given indefinite causal order is physical [29,30]. In quantum computing, the quantum switch can reduce the query complexity for some tasks compared to causally ordered protocols [18,31] -this advantage has been demonstrated for single-qubit control and single-qubit target circuits [32]. In quantum communication, the quantum switch enhances the communication rate beyond the limits of ...

Bit commitment is a fundamental cryptographic task that guarantees a secure commitment between two mutually mistrustful parties and is a building block for many cryptographic primitives, including coin tossing 1, 2 , zero-knowledge proofs 3, 4 , oblivious transfer 5, 6 and secure two-party computation 7 . Unconditionally secure bit commitment was thought to be impossible 8-13 until recent theoretical protocols that combine quantum mechanics and relativity were shown to elude previous impossibility proofs 14-17 . Here we implement such a bit commitment protocol 17 . In the experiment, the committer performs quantum measurements using two quantum key distribution systems 18 and the results are transmitted via free-space optical communication to two agents separated with more 1

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Quantum mechanics provides means of generating genuine randomness that is impossible with deterministic classical processes. Remarkably, the unpredictability of randomness can be certified in a self-testing manner that is independent of implementation devices. Here, we present an experimental demonstration of self-testing quantum random number generation based on an detection-loophole free Bell test with entangled photons. In the randomness analysis, without the assumption of independent identical distribution, we consider the worst case scenario that the adversary launches the most powerful attacks against quantum adversary. After considering statistical fluctuations and applying an 80 Gb × 45.6 Mb Toeplitz matrix hashing, we achieve a final random bit rate of 114 bits/s, with a failure probability less than 10 −5 . Such self-testing random number generators mark a critical step towards realistic applications in cryptography and fundamental physics tests. 2Introduction.-Random numbers are widely used in applications ranging from numerical