Nitrogen Vacancy (NV) center in diamond

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Subproject 3 Quantum Repeaters Report I
nstitute of Quantum Optics and Quantum
Information Austrian Academy of Science, Vienna
Austria Nathan Langford, Vienna
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The team
ELSAG
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Workpackages

• WP0 Workshop Planning Partners Coordination
• WP1 Quantum Channels
• WP2 Sources of entangled photons
• WP3 Long distance fiber-optic quantum relays and
  purification
• WP4 Terrestrial and satellite free-space quantum
  communication
• WP5 Creation of entangled states of single atoms
  and photons by interference

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WP 3.1 Quantum Channels

• M3.1.5 Intra-city test bed for distribution of
  entanglement (m 36)
• Goal Go outside lab into dirty environment

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WP1 Quantum Channels
Test pad for real world quantum channels in a
noisy intra city environment.
Wavefront measurements performed with a shack
hartman detector
Free-Space Platform on the roof of the IQOQI
building in Vienna.
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WP 3.1 Quantum Channels

• M3.1.6 Report on phase noise characteristics in
  installed optical fibres (m 30)
• D3.1.4 Test of 1550 telecom fibres for
  transmission of polarized entangled photons at
  800 nm (m 30)
• Goal Quantify noise in optical fibers

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Phase noise in long fiber interferometers
Motivation Important class of quantum repeaters
architectures requires phase stability
over long fiber links but short time
scales (e.g. DLCZ, Nature 414,413 (2001) )
(i.e. time required to establish
entanglement between remote QM) Goal Quantify
phase noise in long fiber links over short time
scales in realistic environment.
Mach-Zehnder configuration
Sagnac configuration
J. Minár, et al., Phys. Rev. A, 77, 052325 (2008)
The typical time needed for a mean phase change
of 0.1rad is of the order of 100µs.
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Investigation of distribution of polarization
entanglement at 810 nm in standard telecom fibers
Studies so far have revealed a strong temporal
spread between the fiber modes.
A polarisation entangled source at 810nm is used
to study the effect of mode dispersion in
standard telecom fibers.
Temporal mode dispersion in telecom fibers after
2.7 km
In the next step polarization tomography of the
entangled state will be performed with various
fiber lengths (0 - 5km).
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WP 3.2 Advanced sources of entangled photon pairs

• 9 Milestones
• D3.2.3 Report on narrow-band energy time
  photon-pair source using a PPLN waveguide in a
  cavity (m 36)
• D3.2.4 Demonstrate birefringent phase matched
  pair photon generation in microstructured fibre
  (m 36)
• Goal High-Brightness, Narrow-Band
• Entangled Photons from Integrated Sources

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Narrowband sources to meet requirements for
quantum networks
Cavity enhancement set-upFWHM 170MHz, Finesse
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1 ns photon coherence time
FWM in birefringent fibre source of intrinsically
narrow photon pairs
Signal 0.14nm BW
Flat phase- matching curve for signal
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WP 3.2 Advanced sources of entangled photon pairs
M3.2.10 Distribution of 2-photon entanglement
between four users from a single source (m 36)
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Broadband Source of Polarisation Entangled Photon
for Multi-User Distribution

• Passive switching by Wavelength Division
  Multiplexing devices
• Active routing to many users
• Full control of who gets what in the entangled
  network

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Idea Single source will distribute two photon
entanglement to multi user network using WDM
technology
2 x 30mm ppLN waveguides, type-I, centered _at_
1550 nm, pumped at 775nm Broadband SPDC 70nm
30000 photons/s in a 12nm CWDM channel
1531 1571 channel Visibilities (background
subtracted) 92 for 90 basis 91 for -45 basis
1511 1591 channel Visibilities (background
subtracted) 94 for 90 basis 87 for -45 basis
Further work Superconducting detectors to
increase rate Addition of optical switches to
allow sharing of entanglement between any two
users.
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Stable, high fidelity distribution of
entanglement in (WDM) qubit networks
SPDC source 2 crystals (all fiber) 1 crystal
(compact) Photons rate/WDM channel 0.03M/s
(12nm) 0.36M/s (0.8nm) Visibility
(average) gt90 gt90 Active Phase
stabilization yes yes Active Polarization
control yes under way
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Ultra-broadband sources for non classical
applications
Chirped quasi-phase-matched SPDC
Angular dispersion causing front pump
tilt(crystal set between 2 diffraction gratings)
No tilt Dls 96 nm t 13.4 fs (FWHM) With
tilt Dls 465 nm t 4.6 fs (FWHM)
7.1 fs HOM dip ? 300 nm BW
Ultrashort, near transform limited biphotonsTool
for attosecond quantum optics
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WP 3.3 Long distance fiber-optic quantum relays
and purification
M 3.3.5 Fully tested all-fibre CNOT gate (m
30) Goal All-fiber quantum devices
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WP3.3 Bristol work 2008
An integrated CNOT gate realised in Silica on
Silicon
Ideal
Expt
Politi et al SCIENCE VOL 320 2 MAY 2008 647
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All-fibre CNOT gate
Logical basis
Diagonal basis
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WP 3.3 Long distance fiber-optic quantum relays
and purification

• M 3.3.6 Synchronisation of two independent ps
  entangled photon-pair sources via a classical
  optical channel (m 36)
• Synchronisation completed and a HOM dip observed
  with limited visibility. Several problems
  rectified but prototype fibre filters had to be
  returned to the company for repairs which is
  still causing some delays.
• Goal High-visibility interference from
  independent sources

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WP3.3 Long distance fibre-optic quantum relays
purification
3.3.6 Synchronisation of two independent ps
entangled photon-pair sources via a classical
optical channel (M36)
Optical Synchronisation Link
V 26.7 (max 1/3)
30 pm filters. This corresponds to a coherence
length of 3.5 cm and coherence time of 120ps
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WP 3.3 Long distance fiber-optic quantum relays
and purification

• D 3.3.3 Entanglement-Swapping with active
  switching
• (m 36)
• Goal Active control of entanglement distribution

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Switchable entanglement swapping
What has been achieved fast, polarization-indepe
ndent switchable BSM for single photons Next
deliverable Swap the entanglement on demand.
Received the new femto-laser system for the 4
photon source on the second week of Sept 2008,
high-quality 4 photon source is under developing.
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WP 3.4 Terrestrial and satellite free-space
quantum communication
D 3.4.3 Fast random switch of photonic
polarization for long distance Bell experiment (M
36) Goal Integrate fast random switch in long
distance experiments
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Bell test under locality and freedom-of-choice
conditions
Experimental setup

• 19917 coincidences in 2400 sec.
• CHSH inequality Sexp 2.370.02. ? 16 standard
  deviations
• state tomography F?- 88

To be published
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WP 3.5 Creation of entangled states of single
atoms and photons by interference
M 3.5.5 Determine sample parameters for minimal
spectral diffusion of NV resonance frequency (m
30) D 3.5.3 Create transform-limited photons (m
36) Goal Creation of transform limited photons
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WP3.5 USTUTT (Stuttgart)
µK cooling of single nuclear spins in a room
temperature diamond
µK cooling of single nuclear spins in a room
temperature diamond - arXiv0808.0154 Multipartit
e Entanglement Among Single Spins in
DiamondScience 320 1326-1329 (2008)
First test of three-qubits quantum processor in
solid state
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Long coherence time of optical transitions Decay
of coherence is only limited by decay of excited
states (11 ns) Transform-limited photons of
single NVs- key ingredient for entangling two
distant electron-nuclear spin clusters
Batalov et al Phys. Rev. Lett. 100, 077401
(2008)
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W3.1. Quantum Channels M Wave-front distortion
measurements of free-space links for quantum
communication M Integration of superconducting
detectors into existing polarization entangled
systems D Demonstration of polarization
entanglement maintained over 24 hours in optical
fibres distances beyond 20km with high fidelity
gt0.8 W3.2 Advanced sources of entangled photon
pairs M Demonstration of pair-production from
a wave-guide PDC source D Nondegeratrive fempto
second pulse PPKTP entangled source W3.3 Long
distance fiber-optic quantum relays and
purification D Entanglement-swapping with
active switching D Characterisation of photon
pair source for purification D Develop
experiments showing teleportation and
entanglement swapping using fibre pair photon
sources.   W3.4 Terrestrial and satellite
free-space quantum communication D Report on
the design of a prototype of a satellite-based
photonic transceiver M Here we need one
milestone, Please make suggestions   W3.5
Creation of entangled states of single atoms and
photons by interference NO RESPONSE UP TO NOW
FROM STUTTGART