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Author Hosseini, M.; Campbell, G.; Sparkes, B. M.; Lam, P. K.; Buchler, B. C.
Title (down) Unconditional room-temperature quantum memory Type Journal Article
Year 2011 Publication Nature Physics Abbreviated Journal Nat. Phys.
Volume 7 Issue 10 Pages 794-798
Keywords fromIPMRAS
Abstract Just as classical information systems require buffers and memory, the same is true for quantum information systems. The potential that optical quantum information processing holds for revolutionizing computation and communication is therefore driving significant research into developing optical quantum memory. A practical optical quantum memory must be able to store and recall quantum states on demand with high efficiency and low noise. Ideally, the platform for the memory would also be simple and inexpensive. Here, we present a complete tomographic reconstruction of quantum states that have been stored in the ground states of rubidium in a vapour cell operating at around 80 °C. Without conditional measurements, we show recall fidelity up to 98% for coherent pulses containing around one photon. To unambiguously verify that our memory beats the quantum no-cloning limit we employ state-independent verification using conditional variance and signal-transfer coefficients.
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Call Number RPLAB @ gujma @ Serial 824
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Author Vishveshwara, Smitha
Title (down) Topological qubits: A bit of both Type Journal Article
Year 2011 Publication Nature Physics Abbreviated Journal Nat. Phys.
Volume 7 Issue Pages 450–451
Keywords fromIPMRAS
Abstract 'Standard' qubits have been implemented in diverse physical systems. Now, so-called topological qubits are coming into the limelight, and could potentially be used for decoherence-free quantum computing. Coupling these two types of qubit might enable devices that exploit the virtues of both.
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Call Number RPLAB @ gujma @ Serial 825
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Author Mineev, Vladimir P.
Title (down) Superfluid helium: Order in disorder Type Journal Article
Year 2012 Publication Nature Physics Abbreviated Journal Nat. Phys.
Volume 8 Issue Pages 253–254
Keywords fromIPMRAS
Abstract Confining liquid 3He in porous silica aerogel prepared with strong anisotropy stabilizes a state of axial superfluidity.
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Call Number RPLAB @ gujma @ Serial 810
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Author Billangeon, P.-M.; Nakamura, Y.
Title (down) Superconducting devices: Quantum cups and balls Type Journal Article
Year 2011 Publication Nature Physics Abbreviated Journal Nat. Phys.
Volume 7 Issue 8 Pages 594-595
Keywords fromIPMRAS
Abstract A single microwave photon in a superposition of two states of different frequency is now demonstrated using a superconducting quantum interference device to mediate the coupling between two harmonics of a resonator. Such quantum circuits bring closer the possibility of controlling photon-photon interactions at the single-photon level.
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Call Number RPLAB @ gujma @ Serial 820
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Author Haviland, David
Title (down) Superconducting circuits: Quantum phase slips Type Journal Article
Year 2010 Publication Nature Physics Abbreviated Journal Nat. Phys.
Volume 6 Issue Pages 565–566
Keywords fromIPMRAS
Abstract Coulomb interactions can cause a rapid change in the phase of the wavefunction along a very narrow superconducting system. Such a phase slip at the quantum level is now measured in a chain of Josephson junctions.
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Call Number RPLAB @ gujma @ Serial 807
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Author Hanneke, D.; Home, J. P.; Jost, J. D.; Amini, J. M.; Leibfried, D.; Wineland, D. J.
Title (down) Realization of a programmable two-qubit quantum processor Type Journal Article
Year 2010 Publication Nature Physics Abbreviated Journal Nat. Phys.
Volume 6 Issue 1 Pages 13-16
Keywords fromIPMRAS
Abstract The universal quantum computer is a device capable of simulating any physical system and represents a major goal for the field of quantum information science. In the context of quantum information, `universal' refers to the ability to carry out arbitrary unitary transformations in the system's computational space. Combining arbitrary single-quantum-bit (qubit) gates with an entangling two-qubit gate provides a set of gates capable of achieving universal control of any number of qubits, provided that these gates can be carried out repeatedly and between arbitrary pairs of qubits. Although gate sets have been demonstrated in several technologies, they have so far been tailored towards specific tasks, forming a small subset of all unitary operators. Here we demonstrate a quantum processor that can be programmed with 15 classical inputs to realize arbitrary unitary transformations on two qubits, which are stored in trapped atomic ions. Using quantum state and process tomography, we characterize the fidelity of our implementation for 160 randomly chosen operations. This universal control is equivalent to simulating any pairwise interaction between spin-1/2 systems. A programmable multiqubit register could form a core component of a large-scale quantum processor, and the methods used here are suitable for such a device.
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Call Number RPLAB @ gujma @ Serial 801
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Author Baumert, Thomas
Title (down) Quantum technology: Wave packets get a kick Type Journal Article
Year 2011 Publication Nature Physics Abbreviated Journal Nat. Phys.
Volume 7 Issue 5 Pages 373-374
Keywords fromIPMRAS
Abstract Intense femtosecond pulses of infrared light can manipulate molecules. It is now shown that such control even extends to making different molecular eigenstates interfere with each other in a way never considered before -- a potential tool for optically engineered chemical reactions and for ultrafast information encoding and manipulation.
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Call Number RPLAB @ gujma @ Serial 830
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Author Zakka-Bajjani, Eva; Nguyen, François; Lee, Minhyea; Vale, Leila R.; Simmonds, Raymond W.; Aumentado, José
Title (down) Quantum superposition of a single microwave photon in two different 'colour' states Type Journal Article
Year 2011 Publication Nature Physics Abbreviated Journal Nat. Phys.
Volume 7 Issue 8 Pages 599-603
Keywords fromIPMRAS
Abstract Fully controlled coherent coupling of arbitrary harmonic oscillators is an important tool for processing quantum information. Coupling between quantum harmonic oscillators has previously been demonstrated in several physical systems using a two-level system as a mediating element. Direct interaction at the quantum level has only recently been realized by means of resonant coupling between trapped ions. Here we implement a tunable direct coupling between the microwave harmonics of a superconducting resonator by means of parametric frequency conversion. We accomplish this by coupling the mode currents of two harmonics through a superconducting quantum interference device (SQUID) and modulating its flux at the difference (~7GHz) of the harmonic frequencies. We deterministically prepare a single-photon Fock state and coherently manipulate it between multiple modes, effectively controlling it in a superposition of two different 'colours'. This parametric interaction can be described as a beamsplitter-like operation that couples different frequency modes. As such, it could be used to implement linear optical quantum computing protocols on-chip.
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Call Number RPLAB @ gujma @ Serial 822
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Author Ma, Xiao-Song; Dakic, Borivoje; Naylor, William; Zeilinger, Anton; Walther, Philip
Title (down) Quantum simulation of the wavefunction to probe frustrated Heisenberg spin systems Type Journal Article
Year 2011 Publication Nature Physics Abbreviated Journal Nat. Phys.
Volume 7 Issue 5 Pages 399-405
Keywords fromIPMRAS
Abstract Quantum simulators are controllable quantum systems that can reproduce the dynamics of the system of interest in situations that are not amenable to classical computers. Recent developments in quantum technology enable the precise control of individual quantum particles as required for studying complex quantum systems. In particular, quantum simulators capable of simulating frustrated Heisenberg spin systems provide platforms for understanding exotic matter such as high-temperature superconductors. Here we report the analogue quantum simulation of the ground-state wavefunction to probe arbitrary Heisenberg-type interactions among four spin-1/2 particles. Depending on the interaction strength, frustration within the system emerges such that the ground state evolves from a localized to a resonating-valence-bond state. This spin-1/2 tetramer is created using the polarization states of four photons. The single-particle addressability and tunable measurement-induced interactions provide us with insights into entanglement dynamics among individual particles. We directly extract ground-state energies and pairwise quantum correlations to observe the monogamy of entanglement.
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Call Number RPLAB @ gujma @ Serial 842
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Author Perseguers, S.; Lewenstein, M.; Acín, A.; Cirac, J. I.
Title (down) Quantum random networks Type Journal Article
Year 2010 Publication Nature Physics Abbreviated Journal Nat. Phys.
Volume 6 Issue 7 Pages 539-543
Keywords fromIPMRAS
Abstract Quantum mechanics offers new possibilities to process and transmit information. In recent years, algorithms and cryptographic protocols exploiting the superposition principle and the existence of entangled states have been designed. They should allow us to realize communication and computational tasks that outperform any classical strategy. Here we show that quantum mechanics also provides fresh perspectives in the field of random networks. Already the simplest model of a classical random graph changes markedly when extended to the quantum case, where we obtain a distinct behaviour of the critical probabilities at which different subgraphs appear. In particular, in a network of N nodes, any quantum subgraph can be generated by local operations and classical communication if the entanglement between pairs of nodes scales as N-2. This result also opens up new vistas in the domain of quantum networks and their applications.
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Call Number RPLAB @ gujma @ Serial 804
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