Session K22: Spins in Solids for Quantum Information Processing

The birth of quantum networks: merging remote entanglement with local multi-qubit control

The realization of a highly connected network of qubit registers is a central challenge for quantum information processing and long-distance quantum communication. Diamond spins associated with NV centers are promising building blocks for such a network: they combine a coherent spin-photon interface that has already enabled creation of spin-spin entanglement over 1km [1] with a local register of robust and well-controlled nuclear spin qubits for information processing and error correction [2]. We are now entering a new research stage in which we can exploit these features simultaneously and build multi-qubit networks. I will present our latest results towards the first of such experiments: entanglement distillation between remote quantum network nodes. Finally, I will discuss the challenges and opportunities ahead on the road to large-scale networks of qubit registers for quantum computation and communication. [1] B. Hensen et al., Nature 526, 682 (2015). [2] J. Cramer et al., Nature Communications 7, 11526 (2016)   

Quantum Control and Entanglement of Spins in Silicon Carbide

Over the past several decades silicon carbide (SiC) has matured into a versatile material platform for high-power electronics and optoelectronic and micromechanical devices. Recent advances have also established SiC as a promising host for quantum technologies based on the spin of intrinsic defects, with the potential of leveraging existing device fabrication protocols alongside solid-state quantum control. Among these defects are the divacancies and related color centers, which have ground-state electron-spin triplets with coherence times as long as one millisecond and built-in optical interfaces operating near the telecommunication wavelengths. This rapidly developing field has prompted research into the SiC material host to understand how defect-bound electron spins interact with their surrounding nuclear spin bath. Although nuclear spins are a major source of decoherence in color-center spin systems [1], they are also a valuable resource since they can have coherence times that are orders of magnitude longer than electron spins. In this talk I will discuss our recent efforts to interface defect-bound electron spins in SiC with the nuclear spins of naturally occurring 29Si and 13C isotopic defects. I will discuss how the hyperfine interaction can be used to strongly initialize them [2 -- 4], to coherently control them, to read them out, and to produce genuine electron-nuclear ensemble entanglement [5], all at ambient conditions. These demonstrations motivate further research into spins in SiC for prospective quantum technologies. [1] Seo et al., Nat. Commun. 7, 12935 (2016) [2] Falk et al., Phys. Rev. Lett. 114, 247603 (2015). [3] Ivady et al., Phys. Rev. B. 92, 115206 (2015). [4] Ivady et al., arXiv:1605.07931 (2016) [5] Klimov et al., Sci. Adv. 1, e1501015 (2015).   

Realising a 2 Qubit Gate in Silicon with Donor Electron Spins

Extremely long electron spin coherence times have recently been demonstrated in isotopically pure Si-28 [1] making silicon one of the most promising semiconductor materials for spin based quantum information. The two level spin state of single electrons bound to shallow phosphorus donors in silicon in particular provide well defined, reproducible qubits [2] and represent a promising system for a scalable quantum computer in silicon. An important challenge in these systems is the realisation of a two-qubit gate, where we can both position donors with respect to each other for controllable exchange coupling and with respect to charge sensors for individually addressing and reading out the spin state of each donor with high fidelity. To date we have demonstrated using scanning tunneling microscope hydrogen lithography how we can precisely position individual P donors in Si [3] aligned with nanoscale precision to local control gates [4] and can initialize, manipulate, and read-out the spin states [5,6] with high fidelity. We now demonstrate how we can achieve record single-electron readout fidelity for each of two donor based dots of 99.8$\backslash ${\%}, above the surface-code fault tolerant threshold. We show how by engineering the quantum dots to contain multiple donors we can achieve spin lifetimes up to 16 times longer than single donors. Finally we show how by optimising the interdonor separation and using asymmetric confinement potentials we can create controllable exchange coupling in these devices. With the recent demonstration of ultra-low noise in these all epitaxial devices [7] these results confirm the enormous potential of atomic-scale qubits in silicon.\\ \\ $[1]$ J. T. Muhonen et al., Nature Nanotechnology 9, 986 (2014).\newline [2] B.E. Kane, Nature 393, 133 (1998).\newline [3] M. Fuechsle et al., Nature Nanotechnology 7, 242 (2012).\newline [4] B. Weber et al., Science 335, 6064 (2012).\newline [5] H. Buch et al., Nature Communications 4, 2017 (2013).\newline [6] T.F. Watson et al., Physical Review Letters 115, 166806 (2015).\newline [7] S. Shamim et al., Nano Letters 16, 5779 (2016).   

Coherent control of rare earth ions in solids.

Rare earth ions in solids are among the most remarkable quantum system. Record coherence times of a couple of hours and telecom emission wavelengths are only a few of their outstanding properties. Many application require single spin control. In the talk I will describe our attempts to position single rare earth ions with high accuracy and yield [1]. I will then discuss the spin coherence properties of single ions and the correlation of spin state and photon properties [2]. In addition our recent all-optical control of spin coherence [3] suggests that single rare earth ion spins are excellent quantum bits. I will compare their performance with other solid state spin quantum systems. References: [1] Kornher T. et al. Production yield of rare-earth ions implanted into an optical crystal, APL 108, 053108, 2016. [2] Kolesov R. et al. Mapping Spin Coherence of a Single Rare-Earth Ion onto a Single Photon Polarisation, Phys. Rev. Lett. 111, 120502, 2013. [3] Xia, K. et al. All-Optical Preparation of coherent Dark States of a Single Rare Earth Ion Spin in a Crystal, Phys. Rev. Lett. 115, 093602, 2015.   

Light matter quantum interface based on single colour centres in diamond

Efficient interfaces between photons and atoms are crucial for quantum networks and enable nonlinear optical devices operating at the single-photon level. In this talk I will highlight properties of single color centers at low temperatures and show that single SiV and GeV color centers in diamond are promising candidates for creating such interfaces. I will also show experiments towards realization of fully integrated, scalable nanophotonic quantum devices..