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2 g C C 2 g 6 m 6 m Ritter et al., Nature 484, 195 (2012) Trapped Ions/Atoms: Quantum Networks Christian Vzquez, David Nadlinger Quantum Systems for Information Technology, Spring Term 2014 Christian Vzquez, David

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Christian Vázquez, David Nadlinger | 09. 05. 2014 | Quantum Systems for Information Technology, Spring Term 2014

Trapped Ions/Atoms: Quantum Networks

Christian Vázquez, David Nadlinger

6 μm 2g Δ Ω 2g

C

6 μm Ω C Δ

Ritter et al., Nature 484, 195 (2012) 1

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Quantum Systems for Information Technology, Spring Term 2014 Christian Vázquez, David Nadlinger | 09. 05. 2014 |

This Talk

  • Quantum Networks: Why? How?
  • Two Entanglement Generation Experiments:

Moehring et al., “Entanglement of single-atom quantum bits at a distance”, Nature 449, 68 (2007) Ritter et al., “An elementary quantum network of single atoms in optical cavities”, Nature 484, 195 (2012)

  • Results/Comparison
  • Perspectives

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Quantum Systems for Information Technology, Spring Term 2014 Christian Vázquez, David Nadlinger | 09. 05. 2014 |

Why Quantum Networks?

Large number of ions in one trap is not feasible:

  • 1D string -> requirements on trap potential
  • Heating rate increases linearly
  • Mechanical mode density increases

State of the art: ~15 qubits

  • Entanglement of 14 ions

Monz et al., Phys. Rev. Lett. 106, 130506 (2011)

  • Simulations using long chains (~20 ions)
  • C. Monroe and J. Kim,

Science 339, 1164 (2013)

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Quantum Systems for Information Technology, Spring Term 2014 Christian Vázquez, David Nadlinger | 09. 05. 2014 |

  • J. Kimble, Nature 453, 1023 (2008)

Why Quantum Networks?

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k systems of n qubits:

  • With classical links: d = k 2n (dim. of state space)

With quantum links: d = 2nk

  • Multiple qubit entanglement
  • > State transfer, information sharing
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Quantum Systems for Information Technology, Spring Term 2014 Christian Vázquez, David Nadlinger | 09. 05. 2014 |

Requirements for Quantum Networks

We infer the following requirements. For Nodes:

  • Receiving, storing, releasing quantum information

For Channels:

  • Faithfully transmit quantum state between nodes

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Quantum Systems for Information Technology, Spring Term 2014 Christian Vázquez, David Nadlinger | 09. 05. 2014 |

Linking Ion Traps

“Quantum CCD”

Kiepinski, Monroe, Wineland, Nature 417, 709 (2002)

Photons

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Quantum Systems for Information Technology, Spring Term 2014 Christian Vázquez, David Nadlinger | 09. 05. 2014 |

Entangling Atoms using Photons

Heralded entanglement

  • gen. using beamsplitter:

Moehring et al. (2007) Cavity QED: Ritter et al. (2012)

  • C. Monroe and J. Kim, Science 339, 1164 (2013)
  • H. Kimble, Nature 453, 1023 (2008)

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Quantum Systems for Information Technology, Spring Term 2014 Christian Vázquez, David Nadlinger | 09. 05. 2014 |

Entangling Atoms using Photons

Heralded entanglement

  • gen. using beamsplitter:

Moehring et al. (2007) Cavity QED: Ritter et al. (2012)

  • C. Monroe and J. Kim, Science 339, 1164 (2013)
  • H. Kimble, Nature 453, 1023 (2008)

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Quantum Systems for Information Technology, Spring Term 2014 Christian Vázquez, David Nadlinger | 09. 05. 2014 |

12.6 GHz 2.1 GHz F = 1 F = 1 F = 0 F = 0

2S1/2 2P1/2 2D3/2 3D[3/2]1/2

0.86 GHz 2.2 GHz F = 1 F = 0 F = 1 F = 2 369.5 nm 935.2 nm

Repump Laser Excitation Laser Qubit Levels

Beam splitter PBS PBS PMT PMT Yb+ Yb+ 1 m B re re B

B = 0.55 mT

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Moehring (2007): Exp. Setup

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Quantum Systems for Information Technology, Spring Term 2014 Christian Vázquez, David Nadlinger | 09. 05. 2014 |

  • | >

| >

–

| >

| >

|0,0> | >

| >

|1,0> | >

| >

( - ) /2 Discard

12.6 GHz 2.1 GHz

2S1/2 2S1/2 2P1/2 2P1/2

|1, 1> |1,–1> |F=1

  • >

|F=1> |0,0>

  • |1,–1>

|1,0> |1,1> |0,0> |1,0>

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Quantum Systems for Information Technology, Spring Term 2014 Christian Vázquez, David Nadlinger | 09. 05. 2014 | 11

Detecting 2 coincident photons projects atoms into ,

1 2 | | | | (| | | | 1 2(|

  • |
  • + |
  • |
  • |
  • |
  • |
  • |
  • |
  • )

±

1 2 | | ± | |

±

1 2 | | ± | |

Consider input state 50/50 (non-polarizing) beam splitter: where coincident photons “herald” entanglement creation!

atom photon

  • +
  • a

b a b a b a b

symmetric symmetric symmetric antisymmetric

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Quantum Systems for Information Technology, Spring Term 2014 Christian Vázquez, David Nadlinger | 09. 05. 2014 |

Entangling Atoms using Photons

Heralded entanglement

  • gen. using beamsplitter:

Moehring et al. (2007) Cavity QED: Ritter et al. (2012)

  • C. Monroe and J. Kim, Science 339, 1164 (2013)
  • H. Kimble, Nature 453, 1023 (2008)

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Quantum Systems for Information Technology, Spring Term 2014 Christian Vázquez, David Nadlinger | 09. 05. 2014 |

State Transfer, Entangl. Creation

Ideal state transfer follows from adequate Raman pulses: photonic wave packet determined by Ωi(t)

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Cirac, Zøller, Kimble, Mabuchi, Phys. Rev. Lett. 78, 3221 (1997)

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Quantum Systems for Information Technology, Spring Term 2014 Christian Vázquez, David Nadlinger | 09. 05. 2014 |

Ritter (2012): Entangl. Sequence

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Quantum Systems for Information Technology, Spring Term 2014 Christian Vázquez, David Nadlinger | 09. 05. 2014 |

Ritter (2012): Entangl. Sequence

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Quantum Systems for Information Technology, Spring Term 2014 Christian Vázquez, David Nadlinger | 09. 05. 2014 |

Ritter (2012): Entangl. Sequence

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Quantum Systems for Information Technology, Spring Term 2014 Christian Vázquez, David Nadlinger | 09. 05. 2014 |

Ritter (2012): Entangl. Sequence

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Quantum Systems for Information Technology, Spring Term 2014 Christian Vázquez, David Nadlinger | 09. 05. 2014 |

Ritter (2012): Entangl. Sequence

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Quantum Systems for Information Technology, Spring Term 2014 Christian Vázquez, David Nadlinger | 09. 05. 2014 |

Ritter (2012): Entangl. Sequence

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Quantum Systems for Information Technology, Spring Term 2014 Christian Vázquez, David Nadlinger | 09. 05. 2014 |

Ritter (2012): Entangl. Sequence

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Quantum Systems for Information Technology, Spring Term 2014 Christian Vázquez, David Nadlinger | 09. 05. 2014 |

  • Moehring (2007): Only correlations in unrotated basis
  • Ritter (2012): Full state tomography

State Tomography

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0.1 Detected states 0.2 0.3 0.4 Detection probability

  • 0.5

–0.5 LL LR RL RR LL LR RL RR . 4 4 . 4 5 . 7 . 4 – . 4 1 – . 4 1 Re( ρ)

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Quantum Systems for Information Technology, Spring Term 2014 Christian Vázquez, David Nadlinger | 09. 05. 2014 |

  • Moehring (2007): Microwave pulses, different phase
  • Ritter (2012): Extra B field applied for 12.5 µs

Local rotations: fidelity oscillates

22 0.2 0.4 0.6 0.8 1.0 –40 –20 20 40 60 80 100 Probability for odd parity Pulse delay (s)

20 40 60 100 20 40 60 80 Fidelity with respective Bell state (%)

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Quantum Systems for Information Technology, Spring Term 2014 Christian Vázquez, David Nadlinger | 09. 05. 2014 |

Comparison

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Moehring (2008) Ritter (2012) Excitation to upper state with short pulse Photon creation Stimulated Raman process (STIRAP) Interference at 50/50 beam splitter Photon use Raman process at target atom F = 65 ± 3% Fidelity to target state F = 85 ± 1.3 % p = 3.6 ∙ 10-9 Success probability of entanglement scheme p = 0.02 R = 0.118 min-1 Rate of entanglement creation R = 1800 min-1 Coincidence detection Entanglement heralding None

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Quantum Systems for Information Technology, Spring Term 2014 Christian Vázquez, David Nadlinger | 09. 05. 2014 |

Perspectives

  • Review:
  • C. Monroe and J. Kim, Science 339, 1164 (2013)
  • Entanglement by single photon detection

Slodička et al., PRL 110, 083603 (2013)

  • Atom/photon quantum gates

Reiserer et al., Nature 508, 237 (2014) Tiecke et al., Nature 508, 241 (2014)

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ELU ELU ELU ELU N x N optical crossconnect switch

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Quantum Systems for Information Technology, Spring Term 2014 Christian Vázquez, David Nadlinger | 09. 05. 2014 |

Conclusion

  • To build large-scale quantum systems, we need to

create entanglement between distant nodes

  • Two approaches for entangling atoms/ions

discussed:

  • Heralded entanglement creation using beam

splitter (probabilistic)

  • Atom-cavity nodes allowing deterministic

interaction with photons

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