Quantum information processing using frequency control of impurity spins in diamond

Abstract

Spin degrees of freedom of charged nitrogen-vacancy (NV − ) centers in diamond have large decoherence times even at room temperature, can be initialized and read out using optical fields, and are therefore a promising candidate for solid state qubits. Recently, quantum manipulations of NV − -centers using RF fields were experimentally realized. In this paper we show; first, that such operations can be controlled by varying the frequency of the signal, instead of its amplitude, and NV − -centers can be selectively addressed even with spacially uniform RF signals; second, that when several NV − -centers are placed in an off-resonance optical cavity, a similar application of classical optical fields provides a controlled coupling and enables a universal two-qubit gate (CPHASE). RF and optical control together promise a scalable quantum computing architecture.

Hybrid quantum circuits: Superconducting circuits interacting with other quantum systems

“…Schematic diagram of two-level systems inside the oxide tunnel barrier of a Josephson junction. Zagoskin et al (2006) theoretically analyzed the quantum TLSs in current-biased Josephson junctions (CBJJ) and these were studied as qubits and also as quantum memories. The dynamics of the TLS-CBJJ system can be described by the following effective Hamiltonian:…”

“…Quantum dots can be integrated into micropillar cavities (Press et al, 2007;Reithmaier et al, 2004), microdisk cavities (Imamoglu et al, 1999;Peter et al, 2005;Witzany et al, 2011), or photonic crystal cavities (Carter et al, 2012;Faraon et al, 2008;Hennessy et al, 2007;Nomura et al, 2010;Yoshie et al, 2004), and strong coupling with the photon field in the cavity can be achieved. Atomic impurity spins, especially NV centers, can also couple to microsphere cavities (Park et al, 2006), microtoroidal cavities (Chen et al, 2011), or photonic crystal cavities (Su et al, 2009;Tomljenovic-Hanic et al, 2006;Zagoskin et al, 2007).…”

“…Generally, TLSs are regarded as a nuisance because they cause decoherence (Ku and Yu, 2005;Martin et al, 2005). However, it was proposed (Zagoskin et al, 2006), and experimentally demonstrated (Neeley et al, 2008;Sun et al, 2010) that these TLSs, which sometimes have long coherence times, can also be used as quantum memories. This approach provides a new method to utilize TLS defects in solid-state devices.…”

Two-qubit quantum gates for defect qubits in diamond and similar systems

“…The optical transition energy ∆ depends on the local environment of each defect, particularly when the defect is on the surface of a microcavity [18,20,21], and can vary substantially from defect to defect. Typical entangling gate schemes [22,23] operate by bringing the states into and out of resonance with the cavity, thus, switching the interaction on and off to perform the gate. Our approach does not use such control and, hence, does not require resonance between cavity photons and dipole transition lines in each defect.…”

Multiphoton Controllable Transport between Remote Resonators

“…Owing to high speed transmission and negligible interaction with the environment, in the form of flying qubits, photons are the natural candidates for long-distance quantum communication [1][2][3][4][5][6][7]. Alternatively, for short-distance quantum communication inside a quantum computer, the majority of promising channels rely upon the use of solid-state-based devices, including nuclear spins in nuclear magnetic resonance (NMR) [8,9], electron spins of nitrogen-vacancy (NV) colour centers in diamond [10][11][12][13][14][15], and flux qubits in superconductors [16][17][18][19]. Moreover, coupled-resonator arrays (CRAs), being currently explored in various physical systems such as superconducting transmission line resonators [20][21][22][23][24], toroidal microresonators [25][26][27][28] and plasmonic nanoparticle arrays [29], have been attracted much attention in recent years.…”