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Optical cavities and trapped ions:building blocks for quantum networks
Tracy NorthupInstitute for Experimental Physics, University of Innsbruck
Zeiss Symposium 2018: Optics in the Quantum World
• Quantum light fields for computing, communication & simulation
• Classical light fields for manipulation & measurement of matter-based qubits
Here, optical cavities as an interface between quantum light and quantum matter.
What roles does optics play in quantum technology?
Zeiss Symposium 2018 I T. E. Northup I 18.04.2018 Page 2
Ingredients for a quantum network
Photons travelling along quantum channels…
…linking quantum nodes:• generation & measurement
of quantum states• quantum memories• quantum computers
Key concept:Coherent interface between nodes and channels.
H. J. Kimble, Nature 453, 1023 (2008)
Network applications:• quantum communication• quantum sensing• distributed quantum computing
Zeiss Symposium 2018 I T. E. Northup I 18.04.2018 Page 3
» Trapped-ion qubits for quantum information science
» Optical cavities as building blocks for quantum networksEntangling ions and photonsTransferring quantum states between ions and photons
» Outlook: applications for ion-based networks
Zeiss Symposium 2018 I T. E. Northup I 18.04.2018 Page 4
Ions: a highly controllable two-level system.
» Coherence can be preserved for long times in hyperfine and optical qubits
» Deterministic, high-fidelity, coherent manipulation of both individual qubits and gate operations between qubits
» High-fidelity state readout via electron shelving
Trapped ions as quantum bits
32D5/2
729 nm
42P1/2397 nm
40Ca+
42S1/2Linear Paul trap: RF field creates a rotating pseudopotential for charged particles.
DC
DC
RF
RF
GND
GND
Zeiss Symposium 2018 I T. E. Northup I 18.04.2018 Page 5
Two examples of the state of the art:
A platform for quantum computing and metrology
1. Multi-partite entanglement in a register of 20 qubitsN. Friis, O. Marty, C. Maier, C. Hempel, M. Holzäpfel, P. Jurcevic, M. B. Plenio, M. Huber, C. Roos, R. Blatt, and B. Lanyon, Phys. Rev. X 8, 021012 (2018)
• Entanglement characterized for neighboring groups of qubits• Each qubit individually controlled & qubit-qubit interactions turned
on and off
2. Spectroscopy of molecular ions via quantum logicF. Wolf, Y. Wan, J. C. Heip, F. Gebert, C. Shi, P. O. Schmidt, Nature 530, 457 (2016)
• Quantum state of molecular ion measured via its coupling to an atomic ion
ions as sensors: talk today by J. Hecker Denschlag
Zeiss Symposium 2018 I T. E. Northup I 18.04.2018 Page 6
» Trapped-ion qubits for quantum information science
» Optical cavities as building blocks for quantum networksEntangling ions and photonsTransferring quantum states between ions and photons
» Outlook: applications for ion-based networks
Zeiss Symposium 2018 I T. E. Northup I 18.04.2018 Page 7
An ion trap integrated with an optical cavity
Zeiss Symposium 2018 I T. E. Northup I 18.04.2018 Page 8
A Raman process generates single cavity photons
32D5/2
393 nm
854 nm
729 nm
42D1/2397 nm
42P3/2
cavity
laser
40Ca+
42S1/2
Zeiss Symposium 2018 I T. E. Northup I 18.04.2018 Page 9
Entangled ions and photons: a network resource
S
S → DHS → D´V
S → DH + D´V
…the ion and photon are maximally entangled.
D´D
A bichromatic Raman field generates entanglement.
42P3/2
H
V
32D5/242S1/2
Zeiss Symposium 2018 I T. E. Northup I 18.04.2018 Page 10
Entangled ions and photons: a network resource
S
D´D
42P3/2
H
V
32D5/242S1/2
The photon is measured in three orthogonal bases…
…and the ion in three orthogonal bases.
A. Stute et al., Nature 485, 482 (2012)
Zeiss Symposium 2018 I T. E. Northup I 18.04.2018 Page 11
Entangled ions and photons: a network resource
S
D´D
42P3/2
H
V
32D5/242S1/2
…and the ion in three orthogonal bases.
A. Stute et al., Nature 485, 482 (2012)
maximally entangled state: DH + D´V
classical bound: 50%
Zeiss Symposium 2018 I T. E. Northup I 18.04.2018 Page 12
Ion-photon entanglement enables remote entanglement
click! click!
entangled!
Cavities aren’t required…• ions in separate traps
D. L. Moehring et al., Nature 449, 68 (2007) • atomic ensembles, neutral atoms, NV centers, quantum dots, ...
...but they are a means to achieve efficient collection.
Zeiss Symposium 2018 I T. E. Northup I 18.04.2018 Page 13
A similar protocol entangles ions in the same cavity
B. Casabone et al., Phys. Rev. Lett. 111, 100505 (2013)
ion 1: DH + D´Vion 2: DH + D´V
→ detect H & V → DD´ + D´D
We prepare ion–ion entanglement with fidelity ≥ (91.9 ± 2.5)% with respect to a maximally entangled state.
Outlook: cavity-based methods as a route to efficient remote entanglement & teleportation-based networks.
L.-M. Duan, H. J. Kimble, Phys. Rev. Lett. 90, 253601 (2003)
phase
parity
Zeiss Symposium 2018 I T. E. Northup I 18.04.2018 Page 14
An alternative to teleporation: quantum state transferJ. I. Cirac, P. Zoller, H. J. Kimble, H. Mabuchi, Phys. Rev. Lett. 78, 3221 (1997)
neutral atoms:S. Ritter et al., Nature 484, 195 (2012)
TN & R. Blatt, Nature Photon. 8, 256 (2014)
Zeiss Symposium 2018 I T. E. Northup I 18.04.2018 Page 15
A bichromatic Raman process maps the quantum state
S → horizontally polarized photonS´ → vertically polarized photon𝑎𝑎S + 𝑏𝑏S´ → 𝑎𝑎H + 𝑏𝑏V
S´
D
S
42S1/2
32D5/2
42P3/2
A. Stute et al., Nat. Photon. 7, 219 (2013)
Process fidelity: 92%Classical threshold: 50%
Zeiss Symposium 2018 I T. E. Northup I 18.04.2018 Page 16
Addressing decoherence in state-transfer networks
A significant loss mechanism for current experiments: scattering and absorption losses in the cavity.
Can we build networks based on direct state transfer along photonic channels?
We compare two methods for state transfer; one method allows us to suppress these losses.
B. Vogell et al., Quantum Sci. Technol. 2, 045003 (2017)
Zeiss Symposium 2018 I T. E. Northup I 18.04.2018 Page 17
Addressing decoherence in state-transfer networks
J. I. Cirac, P. Zoller, H. J. Kimble, H. Mabuchi, Phys. Rev. Lett. 78, (1997)
T. Pellizzari, Phys. Rev. Lett. 79, 5242 (1997)
Can we build networks based on direct state transfer along photonic channels?
#1 #2
Zeiss Symposium 2018 I T. E. Northup I 18.04.2018 Page 18
Addressing decoherence in state-transfer networksCan we build networks based on direct state transfer along photonic channels?
The key idea: Cavity losses are analogous to spontaneous emission in STIRAP and can be suppressed.
(Channel losses, on the other hand, can’t be suppressed.)
B. Vogell et al., Quantum Sci. Technol. 2, 045003 (2017)
Zeiss Symposium 2018 I T. E. Northup I 18.04.2018 Page 19
» Trapped-ion qubits for quantum information science
» Optical cavities as building blocks for quantum networksEntangling ions and photonsTransferring quantum states between ions and photons
» Outlook: applications for ion-based networks
Zeiss Symposium 2018 I T. E. Northup I 18.04.2018 Page 20
Scaling up cavity-based interfaces
» Smaller cavities → faster interface with higher fidelities
2 cmwaist: 13 µm
0.5 mm
high-finesse mirrors on optical fiber tips, ablated with a CO2 laserD. Hunger et al., New. J. Phys. 12, 065038 (2010)
K. Ott et al., Opt. Express 24, 9839 (2916)
see also: ions + fiber cavities in Bonn (Köhl), Sussex (Keller), Mainz (Schmidt-Kaler)…
» Scaling up ion traps: ongoing research efforts worldwide
HOA2 trap, Sandia National Laboratories
… integrating optics is an important & challenging task.see: work in Chiaverini group at Lincoln Labs on integrated waveguides for ion addressing
Zeiss Symposium 2018 I T. E. Northup I 18.04.2018 Page 21
Towards a quantum internet
Quantum Internet Alliancehttp://quantum-internet.team
This talk: ion-photon interactions at one node
State of the art: two-node experiments
We need:
• multi-node networks over long distances
• quantum repeaters that surpass direct transmission
How to benchmark different experimental platforms?
Network applications beyond quantum key distribution:
What resources are required?
Which applications are suited to few-node networks?
Zeiss Symposium 2018 I T. E. Northup I 18.04.2018 Page 22
Optical cavities provide an interface between ions and photons, enabling building blocks for quantum networks: entanglement and quantum state transfer.
Trapped ions are a promising platform for quantum simulation, computation & sensing. Network connectivity enables distributed applications & quantum communication.
Scaling up from experiments with one and two nodes will require us to address decoherence in quantum nodes and channels.
Zeiss Symposium 2018 I T. E. Northup I 18.04.2018 Page 23
Quantum Light-Matter Interfaces Group
Moonjoo Lee
Florian Kranzl
Konstantin Friebe
Dmitry Bykov
Dario Fioretto
Markus Teller Lorenzo Dania
Pau Mestres
Florian Ong KlemensSchüppert
Matthias Knoll
Pierre Jobez
Zeiss Symposium 2018 I T. E. Northup I 18.04.2018 Page 24
Quantum Optics and Spectroscopy Group
Adiabatic passage: B. Vogell, B. Vermersch, B. Lanyon, C. Muschik @ Innsbruck
Fiber cavities: K. Ott, S. Garcia, J. Reichel @ ENS, Paris
Collaborations
Zeiss Symposium 2018 I T. E. Northup I 18.04.2018 Page 25
Optical cavities and trapped ions:�building blocks for quantum networks��Tracy Northup�Institute for Experimental Physics, University of Innsbruck��Zeiss Symposium 2018: Optics in the Quantum WorldWhat roles does optics play in quantum technology?Ingredients for a quantum networkFoliennummer 4Trapped ions as quantum bitsA platform for quantum computing and metrologyFoliennummer 7An ion trap integrated with an optical cavityA Raman process generates single cavity photonsEntangled ions and photons: a network resourceEntangled ions and photons: a network resourceEntangled ions and photons: a network resourceIon-photon entanglement enables remote entanglementA similar protocol entangles ions in the same cavityAn alternative to teleporation: quantum state transferA bichromatic Raman process maps the quantum stateAddressing decoherence in state-transfer networksAddressing decoherence in state-transfer networksAddressing decoherence in state-transfer networksFoliennummer 20Scaling up cavity-based interfacesTowards a quantum internetFoliennummer 23Quantum Light-Matter Interfaces GroupQuantum Optics and Spectroscopy Group