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Qubit teleportation between non-neighbouring network nodes a, Circuit diagram of the teleportation protocol using notation defined in Fig. 3. m (n) is the number of attempts needed to herald entanglement for the AB (BC) entangled link. See the Supplementary Information for the full circuit diagram. b, Teleported state fidelities for the six cardinal states and their average (Avg.). The grey lines show the expected fidelities from simulations. The dashed lines in b–d represent the classical bound of 2/3. c, Average teleported state fidelity for the different outcomes of the BSM on Charlie. The right-most bar shows the resulting fidelity when no feed-forward operation on Alice would be applied. The numerical values of the bar plots shown in b and c can be found in Extended Data Tables 1 and 2. d, Average state fidelity for a conditional and an unconditional teleportation, for different detection window lengths of the two-node entanglement generation processes. The blue-bordered data point is the same point as shown in b. All error bars represent one standard deviation.
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Future quantum internet applications will derive their power from the ability to share quantum information across the network1,2. Quantum teleportation allows for the reliable transfer of quantum information between distant nodes, even in the presence of highly lossy network connections3. Although many experimental demonstrations have been performe...
Citations
... Different quantum hardware such as solid-state defect centers [5,6], atomic ensembles [7][8][9], trapped ions [10,11] and quantum dots [12] are currently being developed to enable a functional quantum repeater. There exist numerous theoretical proposals for repeater architectures tailored to the specific features of each hardware [13][14][15][16]. ...
... Quantum repeaters based on individual atoms or atom-like defects represent an alternative route [5,6,23]. Near-deterministic single-spin photon transducers, which can transfer quantum information between a photon and a single spin, can be achieved by coupling the atomic system to optical resonators enabling efficient single-photon generation [24][25][26]. ...
Reliable quantum communication over hundreds of kilometers is a daunting yet necessary requirement for a quantum internet. To overcome photon loss, the deployment of quantum repeater stations between distant network nodes is necessary. A plethora of different quantum hardware is being developed for this purpose, each platform with its own opportunities and challenges. Here, we propose to combine two promising hardware platforms in a hybrid quantum repeater architecture to lower the cost and boost the performance of long-distance quantum communication. We outline how ensemble-based quantum memories combined with single-spin photon transducers, which can transfer quantum information between a photon and a single spin, can facilitate massive multiplexing, efficient photon generation, and quantum logic for amplifying communication rates. As a specific example, we describe how a single Rubidium (Rb) atom coupled to nanophotonic resonators can function as a high-rate, telecom-visible entangled photon source with the visible photon being compatible with storage in a Thulium-doped crystal memory (Tm-memory) and the telecom photon being compatible with low loss fiber propagation. We experimentally verify that Tm and Rb transitions are in resonance with each other. Our analysis shows that by employing up to 9 repeater stations, each equipped with two Tm-memories capable of holding up to 625 storage modes, along with four single Rb atoms, one can reach a quantum communication rate of about 10 secret bits per second across distances of up to 1000 km.
... Quantum memory is a basic ingredient for quantum information technology and plays a key role in quantum computing [1,2], communication [3][4][5][6], and networking [5][6][7][8][9][10][11][12][13][14]. In a quantum network based on the quantum repeater architecture, photonic quantum memory serves as the local quantum nodes to connect the communication channels and thus provides the key building block, as shown in Fig. 1(a). ...
Quantum networks can enable various applications such as distributed quantum computing, long-distance quantum communication, and network-based quantum sensing with unprecedented performances. One of the most important building blocks for a quantum network is a photonic quantum memory which serves as the interface between the communication channel and the local functional unit. A programmable quantum memory which can process a large stream of flying qubits and fulfill the requirements of multiple core functions in a quantum network is still to be realized. Here we report a high-performance quantum memory which can simultaneously store 72 optical qubits carried by 144 spatially separated atomic ensembles and support up to a thousand consecutive write or read operations in a random access way, 2 orders of magnitude larger than the previous record. Because of the built-in programmability, this quantum memory can be adapted on demand for several functions. As example applications, we realize quantum queue, stack, and buffer which closely resemble the counterpart devices for classical information processing. We further demonstrate the storage and reshuffle of four entangled pairs of photonic pulses with probabilistic arrival time and arbitrary release order via the memory, which is an essential requirement for the realization of quantum repeaters and efficient routing in quantum networks. Realization of this multipurpose programmable quantum memory thus constitutes a key enabling building block for future large-scale fully functional quantum networks.
... When two or more quantum particles in a many-body system are entangled, the system's wavefunction cannot be factorized as a product of the wavefunctions of its constituents (1). Entanglement has now been established as the driving force behind the stunning development of quantum information science (2)(3)(4)(5)(6)(7). A key example of entanglement emerges in Einstein's photoelectric effect, where photoelectrons and ions form a bipartite system as measurements of the electron's kinetic energy provide information about the state of the ion. ...
Quantum entanglement between the degrees of freedom encountered in the classical world is challenging to observe due to the surrounding environment. To elucidate this issue, we investigate the entanglement generated over ultrafast timescales in a bipartite quantum system comprising two massive particles: a free-moving photoelectron, which expands to a mesoscopic length scale, and a light-dressed atomic ion, which represents a hybrid state of light and matter. Although the photoelectron spectra are measured classically, the entanglement allows us to reveal information about the dressed-state dynamics of the ion and the femtosecond extreme ultraviolet pulses delivered by a seeded free-electron laser. The observed generation of entanglement is interpreted using the time-dependent von Neumann entropy. Our results unveil the potential for using short-wavelength coherent light pulses from free-electron lasers to generate entangled photoelectron and ion systems for studying spooky action at a distance.
... The first demonstration of entanglement swapping was carried out by Pan et al. using polarization-entangled photons [77]. Swapping has been recently applied to connect two spatiallyseparated solid-state quantum memories by telecom links [73], and to entangle non-neighboring Nitrogen Vacancy (NV) qubits in a multinode teleportation network [78]. Teleport Local CZs Figure 3: Examples of teledata and telegate circuits for the application of CZs gates over |t 1 ⟩ and |t 2 ⟩ with the remote state |a⟩ as control. ...
... To this purpose, heralded entanglement of photons emitted after de-excitation from prepared excited states has been shown in trapped-ion qubits [106,116,117], neutral atoms [118] and diamond NV-center qubits [119,120,121,122]. After the subsequent BSM, fidelities to Bell states of up to 88% at 230 m have been demonstrated in trappedions [123], and deterministic qubit state transfer between different NV-center nodes has also been shown [78]. Figure 4 shows a schematic representation of light-matter entanglement swapping by BSM. ...
The emerging field of quantum computing has shown it might change how we process information by using the unique principles of quantum mechanics. As researchers continue to push the boundaries of quantum technologies to unprecedented levels, distributed quantum computing raises as an obvious path to explore with the aim of boosting the computational power of current quantum systems. This paper presents a comprehensive survey of the current state of the art in the distributed quantum computing field, exploring its foundational principles, landscape of achievements, challenges, and promising directions for further research. From quantum communication protocols to entanglement-based distributed algorithms, each aspect contributes to the mosaic of distributed quantum computing, making it an attractive approach to address the limitations of classical computing. Our objective is to provide an exhaustive overview for experienced researchers and field newcomers.
... This progress began with the development of light-matter interfaces for entanglement generation [13,14], followed by the utilization of photons at telecom wavelengths to distribute light-matter entanglement over tens of kilometers of optical fiber [15][16][17][18]. Subsequent achievements have included the generation of high-fidelity entanglement [19][20][21][22] and long-distance entanglement [23][24][25][26] between two distant memories, the construction of the first three-node network [27,28], and the implementation of a first functional quantum repeater node [29][30][31]. ...
Long-distance entanglement distribution is the key task for quantum networks, enabling applications such as secure communication and distributed quantum computing. In this work, we take a crucial step toward this task by sharing entanglement over long optical fibers between a single 87Rb atom and a single photon. High fidelity of the atomic state could be maintained during long flight times through such fibers by prolonging the coherence time of the single atom to 10 ms based on encoding in long-lived states. In addition, the attenuation in the fibers is minimized by converting the wavelength of the photon to the telecom S band via polarization-preserving quantum frequency conversion. These improvements enable us to observe entanglement between the atomic quantum memory and the emitted photons transmitted through standard spooled telecom fibers with a length of 101 km with a fidelity of 70.8±2.4%. This fidelity is comparable to recent demonstrations over 20 km, despite the channel loss now significantly exceeding 20 dB. In fact, now the reduction in fidelity is due to detector dark counts rather than loss of coherence of the atom or photon, proving the suitability of our platform to realize city-to-city-scale quantum network links.
... florian.kaiser@list.lu structures could permit to efficiently orchestrate high-quality photonic interference between multiple emitters 24 . In membranes below 0.7 μm thickness, we observe a tendency for slow spectral wandering. ...
Colour centres in silicon carbide emerge as a promising semiconductor quantum technology platform with excellent spin-optical coherences. However, recent efforts towards maximising the photonic efficiency via integration into nanophotonic structures proved to be challenging due to reduced spectral stabilities. Here, we provide a large-scale systematic investigation on silicon vacancy centres in thin silicon carbide membranes with thicknesses down to 0.25 μm. Our membrane fabrication process involves a combination of chemical mechanical polishing, reactive ion etching, and subsequent annealing. This leads to highly reproducible membranes with roughness values of 3–4 Å, as well as negligible surface fluorescence. We find that silicon vacancy centres show close-to lifetime limited optical linewidths with almost no signs of spectral wandering down to membrane thicknesses of ~0.7 μm. For silicon vacancy centres in thinner membranes down to 0.25 μm, we observe spectral wandering, however, optical linewidths remain below 200 MHz, which is compatible with spin-selective excitation schemes. Our work clearly shows that silicon vacancy centres can be integrated into sub-micron silicon carbide membranes, which opens the avenue towards obtaining the necessary improvements in photon extraction efficiency based on nanophotonic structuring.
... These individual entanglement links between quantum nodes can then be combined to distribute the entanglement through a quantum network [11]. This distributed entanglement has been used to perform unconditional quantum teleportation between nodes without a direct optical link [12]. Overall, these technologies pave the way toward network-based quantum computing [13], entanglement-based quantum communications [14], distributed quantum sensing, and long-distance interferometry [15]. ...
The generation of entanglement between distant quantum systems is at the core of quantum networking. In recent years, numerous theoretical protocols for remote-entanglement generation have been proposed, many of which have been experimentally realized. Here, we provide a modular theoretical framework to elucidate the general mechanisms of photon-mediated entanglement generation between single spins in atomic or solid-state systems. Our framework categorizes existing protocols at various levels of abstraction and allows for combining the elements of different schemes in new ways. These abstraction layers make it possible to readily compare protocols for different quantum hardware. To enable the practical evaluation of protocols tailored to specific experimental parameters, we have devised numerical simulations based on the framework with our codes available online.
... Defect platforms offer an electronic qubit featuring a spin-photon interface that enables the generation of distant entanglement [22,23,24], as well as nuclear spins that serve as the longlived memories needed for information storage and buffering. Several protocols based on remote entanglement or entanglement within the electron-nuclear spin system have already been demonstrated in these platforms, including quantum teleportation [25], quantum error correction [17,18,19], enhanced sensing [26,27,28], and entanglement distillation [29]. The electronnuclear spin entanglement is usually realized through dynamical decoupling (DD) sequences; large entangled states can be created by applying consecutive sequences with the appropriate interpulse spacings. ...
Multipartite entangled states are an essential resource for sensing, quantum error correction, and cryptography. Color centers in solids are one of the leading platforms for quantum networking due to the availability of a nuclear spin memory that can be entangled with the optically active electronic spin through dynamical decoupling sequences. Creating electron-nuclear entangled states in these systems is a difficult task as the always-on hyperfine interactions prohibit complete isolation of the target dynamics from the unwanted spin bath. While this emergent cross-talk can be alleviated by prolonging the entanglement generation, the gate durations quickly exceed coherence times. Here we show how to prepare high-quality GHZ M -like states with minimal cross-talk. We introduce the M -tangling power of an evolution operator, which allows us to verify genuine all-way correlations. Using experimentally measured hyperfine parameters of an NV center spin in diamond coupled to carbon-13 lattice spins, we show how to use sequential or single-shot entangling operations to prepare GHZ M -like states of up to M = 10 qubits within time constraints that saturate bounds on M -way correlations. We study the entanglement of mixed electron-nuclear states and develop a non-unitary M -tangling power which additionally captures correlations arising from all unwanted nuclear spins. We further derive a non-unitary M -tangling power which incorporates the impact of electronic dephasing errors on the M -way correlations. Finally, we inspect the performance of our protocols in the presence of experimentally reported pulse errors, finding that XY decoupling sequences can lead to high-fidelity GHZ state preparation.
... Quantum correlations, a fundamental concept in quantum theory, have been crucial in various quantum information processing and technologies in the past decades [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15]. These include quantum teleportation [1][2][3], quantum dense coding [4], quantum key distribution [5][6][7][8], quantum computing [9,10], quantum repeaters [11,12], and quantum sensors [13][14][15]. ...
... Quantum correlations, a fundamental concept in quantum theory, have been crucial in various quantum information processing and technologies in the past decades [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15]. These include quantum teleportation [1][2][3], quantum dense coding [4], quantum key distribution [5][6][7][8], quantum computing [9,10], quantum repeaters [11,12], and quantum sensors [13][14][15]. However, the interaction or coupling between a quantum system and its surrounding environment often cannot be avoided. ...
In the past decade, there has been significant attention on the sudden transition and freezing phenomena of quantum correlations in open system dynamics. In this study, we aim to explore how the quantum steering ellipsoid can be used to characterize the sudden transition of decoherence. Our findings reveal that the shape of the quantum steering ellipsoid undergoes a qualitative change at the transition point during the decoherence process under two commonly encountered noise channels. This observation provides valuable insights into the connection between the sudden transition of decoherence and the geometric properties of the quantum steering ellipsoid. We gain a deeper understanding of this relationship by visually analyzing the changes in the ellipsoid’s shape. Additionally, we compare these results with those obtained using the one-norm geometric quantum discord. This comparison further validates the significance of the sudden transition observed in the quantum steering ellipsoid and highlights the advantages of using this geometric measure. Overall, our study contributes to the understanding of quantum correlations in open systems and provides a visually appealing and intuitive way to analyze the sudden transitions of decoherence using the quantum steering ellipsoid.
... We characterize any quantum network as "advanced" if it enables protocols and capabilities that go beyond point-to-point QKD [3]. These include teleportation [4,5], entanglement swapping [6], memory-assisted networks [7], and others. Entangled photons are a fundamental resource for such demonstrations, and entanglement distribution is therefore a key component of premier quantum network initiatives including the European Quantum Communication Infrastructure (EuroQCI) project, the Illinois Express Quantum Network (IEQNET), the Chinese Quantum Experiments at Space Scale (QUESS) initiative, the United Kingdom UKQNTel network, and the Washington DC-QNet Research Consortium. ...
Entanglement distribution based on time-bin qubits is an attractive option for emerging quantum networks. We demonstrate a 4.09-GHz repetition rate source of photon pairs entangled across early and late time bins separated by 80 ps. Simultaneous high rates and high visibilities are achieved through frequency multiplexing the spontaneous parametric down conversion output into eight time-bin entangled channel pairs. We demonstrate entanglement visibilities as high as 99.4%, total entanglement rates up to 3.55×10⁶ coincidences/s, and predict a straightforward path towards achieving up to an order of magnitude improvement in rates without compromising visibility. Finally, we resolve the density matrices of the entangled states for each multiplexed channel and express distillable entanglement rates in ebit/s, thereby quantifying the trade-off between visibility and coincidence rates that contributes to useful entanglement distribution. This source is a fundamental building block for high-rate entanglement-based quantum key distribution systems or advanced quantum networks.
