ALBERT

Description: Realizing robust quantum information transfer between long-lived qubit registers is a key challenge for quantum information science and technology. Here we demonstrate unconditional teleportation of arbitrary quantum states between diamond spin qubits separated by 3 meters. We prepare the teleporter through photon-mediated heralded entanglement between two distant electron spins and subsequently encode the source qubit in a single nuclear spin. By realizing a fully deterministic Bell-state measurement combined with real-time feed-forward, quantum teleportation is achieved upon each attempt with an average state fidelity exceeding the classical limit. These results establish diamond spin qubits as a prime candidate for the realization of quantum networks for quantum communication and network-based quantum computing.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Pfaff, W -- Hensen, B J -- Bernien, H -- van Dam, S B -- Blok, M S -- Taminiau, T H -- Tiggelman, M J -- Schouten, R N -- Markham, M -- Twitchen, D J -- Hanson, R -- New York, N.Y. -- Science. 2014 Aug 1;345(6196):532-5. doi: 10.1126/science.1253512. Epub 2014 May 29.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Kavli Institute of Nanoscience Delft, Delft University of Technology, Post Office Box 5046, 2600 GA Delft, Netherlands. ; Element Six, Ltd., Kings Ride Park, Ascot, Berkshire SL5 8BP, UK. ; Kavli Institute of Nanoscience Delft, Delft University of Technology, Post Office Box 5046, 2600 GA Delft, Netherlands. r.hanson@tudelft.nl.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/25082696" target="_blank"〉PubMed〈/a〉

Description: Initialization and read-out of coupled quantum systems are essential ingredients for the implementation of quantum algorithms. Single-shot read-out of the state of a multi-quantum-bit (multi-qubit) register would allow direct investigation of quantum correlations (entanglement), and would give access to further key resources such as quantum error correction and deterministic quantum teleportation. Although spins in solids are attractive candidates for scalable quantum information processing, their single-shot detection has been achieved only for isolated qubits. Here we demonstrate the preparation and measurement of a multi-spin quantum register in a low-temperature solid-state system by implementing resonant optical excitation techniques originally developed in atomic physics. We achieve high-fidelity read-out of the electronic spin associated with a single nitrogen-vacancy centre in diamond, and use this read-out to project up to three nearby nuclear spin qubits onto a well-defined state. Conversely, we can distinguish the state of the nuclear spins in a single shot by mapping it onto, and subsequently measuring, the electronic spin. Finally, we show compatibility with qubit control: we demonstrate initialization, coherent manipulation and single-shot read-out in a single experiment on a two-qubit register, using techniques suitable for extension to larger registers. These results pave the way for a test of Bell's inequalities on solid-state spins and the implementation of measurement-based quantum information protocols.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Robledo, Lucio -- Childress, Lilian -- Bernien, Hannes -- Hensen, Bas -- Alkemade, Paul F A -- Hanson, Ronald -- England -- Nature. 2011 Sep 21;477(7366):574-8. doi: 10.1038/nature10401.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Kavli Institute of Nanoscience Delft, Delft University of Technology, PO Box 5046, 2600 GA Delft, The Netherlands.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/21937989" target="_blank"〉PubMed〈/a〉

Description: Protecting the dynamics of coupled quantum systems from decoherence by the environment is a key challenge for solid-state quantum information processing. An idle quantum bit (qubit) can be efficiently insulated from the outside world by dynamical decoupling, as has recently been demonstrated for individual solid-state qubits. However, protecting qubit coherence during a multi-qubit gate is a non-trivial problem: in general, the decoupling disrupts the interqubit dynamics and hence conflicts with gate operation. This problem is particularly salient for hybrid systems, in which different types of qubit evolve and decohere at very different rates. Here we present the integration of dynamical decoupling into quantum gates for a standard hybrid system, the electron-nuclear spin register. Our design harnesses the internal resonance in the coupled-spin system to resolve the conflict between gate operation and decoupling. We experimentally demonstrate these gates using a two-qubit register in diamond operating at room temperature. Quantum tomography reveals that the qubits involved in the gate operation are protected as accurately as idle qubits. We also perform Grover's quantum search algorithm, and achieve fidelities of more than 90% even though the algorithm run-time exceeds the electron spin dephasing time by two orders of magnitude. Our results directly allow decoherence-protected interface gates between different types of solid-state qubit. Ultimately, quantum gates with integrated decoupling may reach the accuracy threshold for fault-tolerant quantum information processing with solid-state devices.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉van der Sar, T -- Wang, Z H -- Blok, M S -- Bernien, H -- Taminiau, T H -- Toyli, D M -- Lidar, D A -- Awschalom, D D -- Hanson, R -- Dobrovitski, V V -- England -- Nature. 2012 Apr 4;484(7392):82-6. doi: 10.1038/nature10900.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Kavli Institute of Nanoscience, Delft University of Technology, PO Box 5046, 2600 GA Delft, The Netherlands.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/22481361" target="_blank"〉PubMed〈/a〉

Description: Quantum entanglement between spatially separated objects is one of the most intriguing phenomena in physics. The outcomes of independent measurements on entangled objects show correlations that cannot be explained by classical physics. As well as being of fundamental interest, entanglement is a unique resource for quantum information processing and communication. Entangled quantum bits (qubits) can be used to share private information or implement quantum logical gates. Such capabilities are particularly useful when the entangled qubits are spatially separated, providing the opportunity to create highly connected quantum networks or extend quantum cryptography to long distances. Here we report entanglement of two electron spin qubits in diamond with a spatial separation of three metres. We establish this entanglement using a robust protocol based on creation of spin-photon entanglement at each location and a subsequent joint measurement of the photons. Detection of the photons heralds the projection of the spin qubits onto an entangled state. We verify the resulting non-local quantum correlations by performing single-shot readout on the qubits in different bases. The long-distance entanglement reported here can be combined with recently achieved initialization, readout and entanglement operations on local long-lived nuclear spin registers, paving the way for deterministic long-distance teleportation, quantum repeaters and extended quantum networks.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Bernien, H -- Hensen, B -- Pfaff, W -- Koolstra, G -- Blok, M S -- Robledo, L -- Taminiau, T H -- Markham, M -- Twitchen, D J -- Childress, L -- Hanson, R -- England -- Nature. 2013 May 2;497(7447):86-90. doi: 10.1038/nature12016. Epub 2013 Apr 24.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Kavli Institute of Nanoscience Delft, Delft University of Technology, PO Box 5046, 2600 GA Delft, The Netherlands.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/23615617" target="_blank"〉PubMed〈/a〉

Description: More than 50 years ago, John Bell proved that no theory of nature that obeys locality and realism can reproduce all the predictions of quantum theory: in any local-realist theory, the correlations between outcomes of measurements on distant particles satisfy an inequality that can be violated if the particles are entangled. Numerous Bell inequality tests have been reported; however, all experiments reported so far required additional assumptions to obtain a contradiction with local realism, resulting in 'loopholes'. Here we report a Bell experiment that is free of any such additional assumption and thus directly tests the principles underlying Bell's inequality. We use an event-ready scheme that enables the generation of robust entanglement between distant electron spins (estimated state fidelity of 0.92 +/- 0.03). Efficient spin read-out avoids the fair-sampling assumption (detection loophole), while the use of fast random-basis selection and spin read-out combined with a spatial separation of 1.3 kilometres ensure the required locality conditions. We performed 245 trials that tested the CHSH-Bell inequality S 〈/= 2 and found S = 2.42 +/- 0.20 (where S quantifies the correlation between measurement outcomes). A null-hypothesis test yields a probability of at most P = 0.039 that a local-realist model for space-like separated sites could produce data with a violation at least as large as we observe, even when allowing for memory in the devices. Our data hence imply statistically significant rejection of the local-realist null hypothesis. This conclusion may be further consolidated in future experiments; for instance, reaching a value of P = 0.001 would require approximately 700 trials for an observed S = 2.4. With improvements, our experiment could be used for testing less-conventional theories, and for implementing device-independent quantum-secure communication and randomness certification.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Hensen, B -- Bernien, H -- Dreau, A E -- Reiserer, A -- Kalb, N -- Blok, M S -- Ruitenberg, J -- Vermeulen, R F L -- Schouten, R N -- Abellan, C -- Amaya, W -- Pruneri, V -- Mitchell, M W -- Markham, M -- Twitchen, D J -- Elkouss, D -- Wehner, S -- Taminiau, T H -- Hanson, R -- England -- Nature. 2015 Oct 29;526(7575):682-6. doi: 10.1038/nature15759. Epub 2015 Oct 21.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉QuTech, Delft University of Technology, PO Box 5046, 2600 GA Delft, The Netherlands. ; Kavli Institute of Nanoscience Delft, Delft University of Technology, PO Box 5046, 2600 GA Delft, The Netherlands. ; ICFO-Institut de Ciencies Fotoniques, The Barcelona Institute of Science and Technology, 08860 Castelldefels (Barcelona), Spain. ; ICREA-Institucio Catalana de Recerca i Estudis Avancats, Lluis Companys 23, 08010 Barcelona, Spain. ; Element Six Innovation, Fermi Avenue, Harwell Oxford, Didcot, Oxfordshire OX11 0QR, UK.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/26503041" target="_blank"〉PubMed〈/a〉

Description: 〈p〉Quantum entanglement involving coherent superpositions of macroscopically distinct states is among the most striking features of quantum theory, but its realization is challenging because such states are extremely fragile. Using a programmable quantum simulator based on neutral atom arrays with interactions mediated by Rydberg states, we demonstrate the creation of "Schrödinger cat" states of the Greenberger-Horne-Zeilinger (GHZ) type with up to 20 qubits. Our approach is based on engineering the energy spectrum and using optimal control of the many-body system. We further demonstrate entanglement manipulation by using GHZ states to distribute entanglement to distant sites in the array, establishing important ingredients for quantum information processing and quantum metrology.〈/p〉

Description: One of the most striking features of quantum mechanics is the profound effect exerted by measurements alone. Sophisticated quantum control is now available in several experimental systems, exposing discrepancies between quantum and classical mechanics whenever measurement induces disturbance of the interrogated system. In practice, such discrepancies may frequently be explained...