Person: Kessler, Eric
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Kessler
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Eric
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Kessler, Eric
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Publication A quantum network of clocks(Springer Nature, 2014) Kómár, P.; Kessler, Eric; Bishof, M.; Jiang, L.; Sørensen, A. S.; Ye, J.; Lukin, MikhailThe development of precise atomic clocks plays an increasingly important role in modern society. Shared timing information constitutes a key resource for navigation with a direct correspondence between timing accuracy and precision in applications such as the Global Positioning System. By combining precision metrology and quantum networks, we propose a quantum, cooperative protocol for operating a network of geographically remote optical atomic clocks. Using nonlocal entangled states, we demonstrate an optimal utilization of global resources, and show that such a network can be operated near the fundamental precision limit set by quantum theory. Furthermore, the internal structure of the network, combined with quantum communication techniques, guarantees security both from internal and external threats. Realization of such a global quantum network of clocks may allow construction of a real-time single international time scale (world clock) with unprecedented stability and accuracy.Publication Quantum Error Correction for Metrology(American Physical Society (APS), 2014) Kessler, Eric; Lovchinsky, Igor; Sushkov, Alexander; Lukin, MikhailWe propose and analyze a new approach based on quantum error correction (QEC) to improve quantum metrology in the presence of noise. We identify the conditions under which QEC allows one to improve the signal-to-noise ratio in quantum-limited measurements, and we demonstrate that it enables, in certain situations, Heisenberg-limited sensitivity. We discuss specific applications to nanoscale sensing using nitrogen-vacancy centers in diamond in which QEC can significantly improve the measurement sensitivity and bandwidth under realistic experimental conditions.Publication Heisenberg-Limited Atom Clocks Based on Entangled Qubits(American Physical Society (APS), 2014) Kessler, Eric; Komar, Peter; Bishof, M.; Jiang, L.; Sørensen, A. S.; Ye, J.; Lukin, MikhailWe present a quantum-enhanced atomic clock protocol based on groups of sequentially larger Greenberger-Horne-Zeilinger (GHZ) states that achieves the best clock stability allowed by quantum theory up to a logarithmic correction. Importantly the protocol is designed to work under realistic conditions where the drift of the phase of the laser interrogating the atoms is the main source of decoherence. The simultaneous interrogation of the laser phase with a cascade of GHZ states realizes an incoherent version of the phase estimation algorithm that enables Heisenberg-limited operation while extending the coherent interrogation time beyond the laser noise limit. We compare and merge the new protocol with existing state of the art interrogation schemes, and identify the precise conditions under which entanglement provides an advantage for clock stabilization: it allows a significant gain in the stability for short averaging time.Publication Optical Superradiance from Nuclear Spin Environment of Single-Photon Emitters(American Physical Society (APS), 2010) Kessler, Eric; Yelin, Susanne; Lukin, Mikhail; Cirac, J. I.; Giedke, G.We show that superradiant optical emission can be observed from the polarized nuclear spin ensemble surrounding a single-photon emitter such as a single quantum dot or nitrogen-vacancy center. The superradiant light is emitted under optical pumping conditions and would be observable with realistic experimental parameters.Publication Long-distance entanglement distribution using individual atoms in optical cavities(American Physical Society (APS), 2015) Borregaard, Johannes; Komar, Peter; Kessler, Eric; Lukin, Mikhail; Sørensen, A. S.Individual atoms in optical cavities can provide an efficient interface between stationary qubits and flying qubits (photons), which is an essential building block for quantum communication. Furthermore, cavity-assisted controlled-not (cnot) gates can be used for swapping entanglement to long distances in a quantum repeater setup. Nonetheless, dissipation introduced by the cavity during the cnot may increase the experimental difficulty in obtaining long-distance entanglement distribution using these systems. We analyze and compare a number of cavity-based repeater schemes combining various entanglement generation schemes and cavity-assisted cnot gates. We find that a scheme, where high-fidelity entanglement is first generated in a two-photon detection scheme and then swapped to long distances using a recently proposed heralded controlled-Z (cz) gate, exhibits superior performance compared to the other schemes. The heralded gate moves the effect of dissipation from the fidelity to the success probability of the gate thereby enabling high-fidelity entanglement swapping. As a result, high-rate entanglement distribution can be achieved over long distances even for low cooperativities of the atom-cavity systems. This high-fidelity repeater is shown to outperform the other cavity-based schemes by up to two orders of magnitude in the rate for realistic parameters and large distances (1000 km).Publication Universal Quantum Transducers Based on Surface Acoustic Waves(American Physical Society (APS), 2015) Schuetz, M. J. A.; Kessler, Eric; Giedke, G.; Vandersypen, L. M. K.; Lukin, Mikhail; Cirac, J. I.We propose a universal, on-chip quantum transducer based on surface acoustic waves in piezoactive materials. Because of the intrinsic piezoelectric (and/or magnetostrictive) properties of the material, our approach provides a universal platform capable of coherently linking a broad array of qubits, including quantum dots, trapped ions, nitrogen-vacancy centers, or superconducting qubits. The quantized modes of surface acoustic waves lie in the gigahertz range and can be strongly confined close to the surface in phononic cavities and guided in acoustic waveguides. We show that this type of surface acoustic excitation can be utilized efficiently as a quantum bus, serving as an on-chip, mechanical cavity-QED equivalent of microwave photons and enabling long-range coupling of a wide range of qubits.Publication Heralded Quantum Gates with Integrated Error Detection in Optical Cavities(American Physical Society (APS), 2015) Borregaard, Johannes; Komar, Peter; Kessler, Eric; Sørensen, A. S.; Lukin, MikhailWe propose and analyze heralded quantum gates between qubits in optical cavities. They employ an auxiliary qubit to report if a successful gate occurred. In this manner, the errors, which would have corrupted a deterministic gate, are converted into a nonunity probability of success: once successful, the gate has a much higher fidelity than a similar deterministic gate. Specifically, we describe that a heralded, near-deterministic controlled phase gate (CZ gate) with the conditional error arbitrarily close to zero and the success probability that approaches unity as the cooperativity of the system, C, becomes large. Furthermore, we describe an extension to near-deterministic N-qubit Toffoli gate with a favorable error scaling. These gates can be directly employed in quantum repeater networks to facilitate near-ideal entanglement swapping, thus greatly speeding up the entanglement distribution.