Building Atom-Photon Networks with Trapped Ions
Trapped ion quantum bits can be linked through a photonic quantum channel, creating long-distance entanglement between quantum memories, quantum networks, and distributed quantum computers.
We are investigating the creation of atom-photon networks using the combination of probabilistic atom-photon entanglement together with deterministic atom-atom entanglement. Ions and photons make an ideal pair for a quantum network which needs both stationary memory qubits and flying communication qubits. The long coherence times of trapped ions make them stand out as the state of the art quantum memory and the fast speed at which photons travel make them the ideal candidate for communication qubits.
In order to entangle two remote ions, each ion is first entangled with an emitted photon. Direct entanglement between "stationary" (ion) and "flying" (photon) qubits was first observed in our lab in 2004 (Nature 428, 153 (2004)).
The photons are collected and directed to a 50:50 beamsplitter. Due to the quantum interference of the photons (Nature Physics 3, 538 (2007)), only an antisymmetric photonic state will result in a simultaneous detection at both output ports of the beamsplitter. It is this "double-click" of the detectors that heralds the entanglement of the two ions. Thus, it is the simultaneous destruction of the photons that lets us know that the ions are now entangled (Nature 449, 68 (2007)).
This entanglement between distant ions was used recently to carry out a teleportation protocol, (Science 323, 486 (2009)), which was the first experiment to demonstrate quantum teleportation between atomic qubits separated by a macroscopic distance.
In order to use this type of photon mediated entanglement for a scalable quantum network, each node in the network must contain two ions. The two ions are used separately to create entanglement with neighboring nodes in the network and then the entire network is linked by carrying out deterministic entangling operations within each node. After establishing the high fidelity of the photon-mediated entanglement protocol, (PRL 102, 250502 (2009)), we are now developing a method of carrying the deterministic entangling operations needed to complete the network.
Deterministic entangling operations in trapped ion systems are carried out by using "spin-dependent" forces which couple the internal states of the individual ions to the collective motion shared among nearby ions. Traditionally, these operations are carried out using continuous wave lasers, but our group has recently been able to simplify these procedures by using a mode-locked pulsed laser. In the regime where many pulses are needed to flip the qubit state of the ion, a train of pulses creates an optical frequency comb. The large bandwidth and spectral purity of the optical frequency comb can be used to deterministically entangle neighboring ions and provides an entirely new structure for creating and probing quantum coherence(arXiv:1001-2127, (2010)).
"Review: Quantum Logic Between Distant Trapped Ions,"S. Olmschenk, D. Hayes, D. N. Matsukevich, P. Maunz, D. L. Moehring, and C. Monroe, quant-ph/0907.1702 (2009).
"Protocols and Techniques for a Scalable Atom–Photon Quantum Network,"L. Luo, D. Hayes, T.A. Manning, D.N. Matsukevich, P. Maunz, S. Olmschenk, J.D. Sterk, and C. Monroe, Fortschritte der Physik 57,11-12 (2009).
"A Heralded Quantum Gate Between Remote Quantum Memories,"P. Maunz, S. Olmschenk, D. Hayes, D. Matsukevich, L.-M. Duan and C. Monroe, PRL 102, 250502 (2009).
"Quantum Teleportation between Distant Matter Qubits,"S. Olmschenk, D. Matsukevich, P. Maunz, D. Hayes, L.-M. Duan and C. Monroe, Science 323, 486 (2009).
"Bell Inequality Violation with Two Remote Atomic Qubits," D. Matsukevich, P. Maunz, D. L. Moehring, S. Olmschenk, and C. Monroe, Phys. Rev. Lett. 100, 150404 (2008).
"Manipulation and Detection of a Trapped Yb+ Hyperfine Qubit," S. Olmschenk, K. C. Younge, D. L. Moehring, D. Matsukevich, P. Maunz, and C. Monroe, Phys. Rev. A 76, 052314 (2007).
"Entanglement of single-atom quantum bits at a distance," D. L. Moehring, P. Maunz, S. Olmschenk, K. C. Younge, D. N. Matsukevich, L.-M. Duan, and C. Monroe, Nature 449, 68 (2007).
"Robust Quantum Information Processing with Atoms, Photons, and Atomic Ensembles," L.-M. Duan and C. Monroe, Advances in Atomic, Molecular, and Optical Physics, vol. 55, E. Arimondo, P.R. Berman and C.C. Lin, eds. (Elsevier, 2007), pp. 419-464.
"Quantum interference of photon pairs from two remote trapped atomic ions," P. Maunz, D. L. Moehring, S. Olmschenk, K. C. Younge, D. N. Matsukevich and C. Monroe, Nature Physics 3, 538 (2007).
Quantum Networking with Photons and Trapped Atoms, D. L. Moehring, M. J. Madsen, K. C. Younge, R. N. Kohn, Jr., P. Maunz, L.-M. Duan, C. Monroe, and B. B. Blinov, J. Opt. Soc. Am. B 24, 300 (2007).
Quantum Interference of Photon Pairs from Two Trapped Atomic Ions, P. Maunz, D. L. Moehring, M. J. Madsen, R. N. Kohn, Jr., K. C. Younge, and C. Monroe, quant-ph/0608047 (2006).
Probabilistic Quantum Gates between Remote Atoms through Interference of Optical Frequency Qubits, L.-M. Duan, M. J. Madsen, D. L. Moehring, P. Maunz, R.N. Kohn, Jr., and C. Monroe, Phys. Rev. A 73, 062324 (2006).
Ultrafast Coherent Coupling of Atomic Hyperfine and Photon Frequency Qubits, M. J. Madsen, D. L. Moehring, P. Maunz, R.N. Kohn, Jr., L.-M. Duan, and C. Monroe, Phys. Rev. Lett. 97, 040505 (2006).
Experimental Bell Inequality Violation with an Atom and a Photon, D.L. Moehring, M.J. Madsen, B.B. Blinov, and C. Monroe, Phys. Rev. Lett. 93, 090410 (2004)
Scalable Trapped Ion Quantum Computation with a Probabilistic Ion-Photon Mapping, L.-M. Duan, B.B. Blinov, D.L. Moehring, and C. Monroe, Quantum Inf. Comput. 4, 165 (2004)
Observation of Entanglement Between a Single Trapped Atom and a Single Photon, B.B. Blinov, D.L. Moehring, L.-M. Duan, and C. Monroe, Nature (London) 428, 153 (2004)
The Trap that Russ Built, by Boris Blinov