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A quantum repeater network formed with hybrid NV diamond modules (Conference Presentation)

Kae Nemoto, Michael Trupke, Burkhard Scharfenberger, Jörg Schmiedmayer, Michael Hanks, W. J. Munro

Published Dec 7, 2016• 0 citations
Publisher

Abstract

We present new quantum repeater architectures based on optical modules with NV diamond centers to highlight how physical properties of these optical modules change the operations, performance and limitations of the quantum repeater systems.We focus on two different approaches to construct optical modules, and see how the properties of modules propagate to the total system. The first approach to construct the optical module is to utilize the conditional refection dependent on the electron state of the single NV center in the cavity, and the other approach is to use absorption induced teleportation from an incoming photon to the nuclear spin of the NV center. To characterize a quantum repeater system, the processes and protocols associated with photons are important.As photons are not reliable as an information carrier, i.e. quantum manipulations associated with photons are not deterministic, and the protocols and manipulations rely on post-selection to keep the fidelity of the quantum information.Post-selection is essential in quantum communications based on photons to maintain the fidelity of the communication, however it restricts the architecture of the system to be tolerant to probabilistic gates. This factor is cost intensive and is the key for the architectures to be scalable.We show that the details of how the scalability of the architectures can be affected by physical parameters of the modules.

DOI
10.1117/12.2237123

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We present new quantum repeater architectures based on optical modules with NV diamond centers to highlight how physical properties of these optical modules change the operations, performance and limitations of the quantum repeater systems.We focus on two different approaches to construct optical modules, and see how the properties of modules propagate to the total system. The first approach to construct the optical module is to utilize the conditional refection dependent on the electron state of the single NV center in the cavity, and the other approach is to use absorption induced teleportation from an incoming photon to the nuclear spin of the NV center. To characterize a quantum repeater system, the processes and protocols associated with photons are important.As photons are not reliable as an information carrier, i.e. quantum manipulations associated with photons are not deterministic, and the protocols and manipulations rely on post-selection to keep the fidelity of the quantum information.Post-selection is essential in quantum communications based on photons to maintain the fidelity of the communication, however it restricts the architecture of the system to be tolerant to probabilistic gates. This factor is cost intensive and is the key for the architectures to be scalable.We show that the details of how the scalability of the architectures can be affected by physical parameters of the modules.
In this article we present a simple repeater scheme based on the negatively-charged nitrogen vacancy centre in diamond. Each repeater node is built from modules comprising an optical cavity containing a single NV(-), with one nuclear spin from (15)N as quantum memory. The module uses only deterministic processes and interactions to achieve high fidelity operations (>99%), and modules are connected by optical fiber. In the repeater node architecture, the processes between modules by photons can be in principle deterministic, however current limitations on optical components lead the processes to be probabilistic but heralded. Our resource-modest repeater architecture contains two modules at each node, and the repeater nodes are then connected by entangled photon pairs. We discuss the performance of such a quantum repeater network with modest resources and then incorporate more resource-intense strategies step by step. Our architecture should allow large-scale quantum information networks with existing or near future technology.
Quantum repeaters are essential for overcoming the exponential photon loss that limits entanglement generation over long distances in quantum networks. An absorption-emission-based quantum repeater exploits the fundamental light-matter interactions of a diamond nitrogen-vacancy (NV) center---photon absorption and photon emission---to transfer a quantum state from an absorbed photon to an emitted photon, offering a scalable architecture that operates without photon interference between remote nodes. Here we demonstrate an absorption-emission-based quantum repeater node using a single NV center, realizing the complete single-node operation in which heralded photon-to-memory quantum state transfer, repeat-until-success (RUS) emission of a spin-entangled photon, and quantum teleportation of the memory state onto the emitted photon constitute the essential repeater operation. By characterizing the complete repeater operation as a quantum channel from the absorbed photon to the emitted photon via quantum process tomography, we obtain a process fidelity of 78%. This demonstration establishes the absorption-emission approach as a fundamental building block for scalable quantum repeater architectures and paves the way toward practical long-distance quantum networks.
We present a quantum repeater architecture using nitrogen-vacancy (NV) diamond based quantum information devices. The NV-diamond based device consists of a single negatively charged NV (NV-) center and an optical cavity. The electron of the NV center is an interface to light to be used to distribute long-distance entanglement as well as entanglement bonds for cluster state operation at each nodes. The nuclear spin-1=2 of nitrogen 15 can be used as memory. Based on this device, A scheme with as small as 10 devices to a scalable architecture is constructed, showing the necessary node technology as well as the performance such quantum communication systems.
The complex environment of solid-state quantum bits is generally believed to pose a difficult challenge for solid state realizations of quantum information science. Close study of single electronic spins associated with the nitrogen-vacancy (NV) center in diamond has shown how a complex environment -- in this case a spin-bath formed by carbon-13 isotopic impurities -- may be understood and even controlled. Specifically, we show that optical and microwave excitation of the NV center can be used to perform robust initialization, manipulation, and measurement of the two-qubit register formed by the electronic spin and its nearest-neighbor carbon-13 nuclear spin. These few-qubit registers may be used as a basis for scalable quantum information systems provided that one can identify a means to connect different registers. For an optically active system such as the NV center, photons provide a natural medium for inter- register communication, and we discuss initial experiments studying the possibility of quantum optical interconnects. Such an optically-connected few-qubit register offers a flexible hardware for both quantum computation and long-distance quantum communication; in particular, it may allow realization of a solid-state quantum repeater.
A quantumnetwork would allow the distribution of a quantum state over many spatially separated quantum nodes which individually possess the ability to generate, process and store quantum information. Connecting these nodes through quantum communication channels would enable sending quantum information over arbitrarily long distances, secret key distribution with guaranteed secure communication and distributed quantum computing. An appealing platform for implementation of quantum networks is the nitrogen-vacancy (NV) center in diamond. An NV center is an optically active defect in diamond created by the substitution of two adjacent carbon atoms in the diamond crystal matrix by a nitrogen atom and a neighboring vacancy. The NV center fits remarkably well in the described quantum network framework. Its electronic spin can be optically initialized, read out in a single shot, coherently manipulated and coupled to the nearby carbon-13 nuclear spins. These properties represent necessary ingredients of a multi-qubit quantum node. The possibility of the entanglement between the state of the NV center spin and a photon establishes a photonic quantum link which can enable the entanglement of the quantum nodes, forming a quantum network. First building blocks of the proposed quantum networks based on NV centers were demonstrated by performing entanglement between two distant NV centers separated by more than a kilometer. However, the current success rate of the entangling protocols is greatly reduced due to the low emission probability of the NV center photons into the resonant zero phonon line (ZPL) and the inefficient photon extraction from the diamond. This is the central problem which prevents promoting our experiments beyond proof-of-principle demonstration towards practical implementation of the proposed quantumnetworks. The goal of this thesis is tackling these issues by coupling NV centers to optical cavities which would greatly increase the rate of generation and collection of the ZPL photons through themechanism of Purcell enhancement. The design and the fabrication of the components constituting a diamond-basedFabry-Perot microcavity, as used in this thesis, are described in Chapter 4. For large enhancement of the NV center resonant emission, a low cavity mode volume is necessary. This is achieved by inserting a micrometers thin diamond slab into the cavity architecture; we present the fabrication details of such samples. Chapter 5 describes the fabrication of an integrated platform for microwave signal delivery to the NV centers within a diamond membrane in the cavity architecture. Microwave striplines and arrays of unique markers are embedded in the mirror onto which the diamond is bonded. We investigate the mirror optical properties post fabrication and find that the fabrication method preserves the mirror optical performance. We describe the diamond bonding method and demonstrate addressing of the NV center spin. In Chapter 6 we probe the properties of the cavity with the embedded diamond membrane through measurements of the cavity finesse. We investigate the cavity finesse dependence on length, mode structure and temperature. We further explore the operation at cryogenic temperatures by probing the effect of cryostation vibration on the cavity linewidth. Finally, in Chapter 7 we discuss ways of improving the existing experimental capabilities, outline the first steps for demonstrating enhancement of the NV center resonant emission and suggest future experiments that can be performed with this system. We conclude that coupling of the NV centers to the cavities developed in this research could lead to an increase of remote entanglement success rates by more than three orders of magnitude.
This presentation will describe several recent results relevant to photonic networks incorporating NV centers. The first experiment relates to the intrinsic properties of NV centers in bulk diamond. An important question is what temperatures are required to emit indistinguishable photons that carry information about the electron spin state of the NV center. While the long-lived coherence in the ground-state spin sublevels persists up to room temperature, transform-limited optical transitions have been observed only at liquid-helium temperatures due to decoherence within the excited states. Recent experiments have shown that this line broadening is due in large part to population relaxation between the two orbital branches which occurs through a two-phonon process. It is difficult to conceive of an entanglement formation scheme that is insensitive to this process, and it appears most likely that a quantum-optical network based on NV centers will have to operate at liquid helium temperatures. This presentation will also summarize our latest results on coupling NV centers to optical cavities, including, for example, hybrid GaP/diamond microdisk cavities with mode volumes of a few cubic wavelengths and experimental quality factors above 25000.