Spins in diamond are promising candidates for building quantum networks, as they combine a long-lived electronic spin with a robust optical transition. Moreover, nuclear spins close to the NV center can be used as qubits, forming small local quantum registers. We aim to generate and detect long-distance entanglement, and use this to perform proof-of-principle demonstrations of the basic elements for quantum information processing, such as long-distance quantum teleportation.
Quantum entanglement between spatially separated objects is one of the most intriguing phenomena in physics. The outcomes of independent measurements on entangled objects show correlations that cannot be explained by classical physics. We have entangled two NV centers in diamonds that are separated by a three-meter distance. This entanglement was achieved by first entangling the spin state of each NV center with a single photon, and a subsequent joint measurement of the photons.
H. Bernien, B. Hensen, W. Pfaff, G. Koolstra, M. S. Blok, L. Robledo, T. H. Taminiau, M. Markham, D. J. Twitchen, L. Childress, R. Hanson, arXiv (2013)
Two-photon quantum interference
When two indistinguishable photons overlap on a beam splitter they show a very surprising behavior: They pair up and leave into the same output port. We observe this interference with photons emitted from two NV centers.
Projective read-out of a solid-state quantum register
Projective readout of the electron spin of a single NV center in diamond is achieved by resonant optical excitation. In combination with hyperfine-mediated quantum gates, this readout enables us to prepare and measure the state of multiple nuclear spin qubits with high fidelity.
Coherent control of the optical transition of single NV centers
We use resonant excitation to observe optical Rabi oscillations of a single NV center. Decoherence effects are studied and a scheme is demonstrated that extends the coherence time.
H. Bernien, L. Childress, L. Robledo, M. Markham, D. Twitschen, R. Hanson, Phys. Rev. Lett. 105, 177403 (2010).\