A critical requirement for diverse applications in Quantum Information
Science is the capability to disseminate quantum resources over complex quantum
networks. For example, the coherent distribution of entangled quantum states
together with quantum memory to store these states can enable scalable
architectures for quantum computation, communication, and metrology. As a
significant step toward such possibilities, here we report observations of
entanglement between two atomic ensembles located in distinct apparatuses on
different tables. Quantum interference in the detection of a photon emitted by
one of the samples projects the otherwise independent ensembles into an
entangled state with one joint excitation stored remotely in 10^5 atoms at each
site. After a programmable delay, we confirm entanglement by mapping the state
of the atoms to optical fields and by measuring mutual coherences and photon
statistics for these fields. We thereby determine a quantitative lower bound
for the entanglement of the joint state of the ensembles. Our observations
provide a new capability for the distribution and storage of entangled quantum
states, including for scalable quantum communication networks .Comment: 13 pages, 4 figures Submitted for publication on August 31 200

A Aspect

A Kuzmich

B Julsgaard

BB Blinov

C Langer

C. W. Chou

CH van der Wal

CW Chou

D Copsey

D Felinto

D. Felinto

DN Matsukevich

G Giovannetti

H Haffner

H-J Briegel

H. de Riedmatten

H. J. Kimble

I Marcikic

JF Clauser

L-M Duan

MA Nielsen

MD Eisaman

QA Turchette

S van Enk

S. J. van Enk

S. V. Polyakov

SV Polyakov

V Balic

W Jiang

WK Wootters

ZY Ou

English

arXiv

We report the observation of heralded entanglement between remote atomic ensembles. The detection of an emitted photon projects the ensembles into an entangled state with one joint excitation stored in the whole system

de Riedmatten, H.

Chou, C. W.

Felinto, D.

Polyakov, S. V.

van Enk, S. J.

Kimble, H. J.

Caltech Authors - Main

Measurement Induced Entanglement for Excitation Stored in 
Remote Atomic Ensembles 
H.de Riedmatten1, C.W Chou1, D. Felinto1, S.V. Polyakov1, S.J. van Enk2 and H.J. Kimble1
1. Norman Bridge Laboratory of Physics 12-33, California Institute of Technology, Pasadena, California 91125, United States 
2. Bell Labs, Lucent Technologies, Room 1D-428, 600-700 Mountain Avenue, Murray Hill, New Jersey 07974, USA 
hugues@caltech.edu
Abstract: We report the observation of heralded entanglement between remote atomic 
ensembles. The detection of an emitted photon projects the ensembles into an entangled state 
with one joint excitation stored in the whole system.  
©2006 Optical Society of America 
OCIS code: (270.0270) Quantum Optics 
A critical requirement for diverse applications in Quantum Information Science is the capability to disseminate 
quantum resources over complex quantum networks. This requires the realization of a quantum memory that would 
allow the storage and retrieval of quantum states. Atomic ensembles appear to be a promising candidate for this task 
[1].  In this contribution we report observations of entanglement between two atomic ensembles located on different 
tables in distinct apparatuses separated by 2.8 meters [2]. Quantum interference in the detection of a photon emitted by 
one of the samples projects the otherwise independent ensembles into an entangled state with one joint excitation 
stored remotely in ~105 atoms at each site. After a delay of 1 μs to demonstrate quantum memory, we confirm 
entanglement by mapping the state of the atoms to optical fields and by measuring mutual coherences and photon 
statistics for these fields. We thereby determine a quantitative lower bound for the entanglement of the joint state of the 
ensembles.  
A simple schematic of our experiment is presented in Fig. 1.  The protocol starts by illuminating the two 
ensembles simultaneously with a weak “write” pulse, such that the probability of creating more than one excitation in 
the symmetric collective mode [1] of each ensemble by spontaneous Raman scattering is very low. (see Fig 1a) 
Entanglement between the L, R ensembles is created by combining the output Stokes fields 1L and 1R on the beam 
splitter BS1, with outputs directed to two detectors D1a and D1b. For small excitation probability and with unit overlap 
of the fields at BS1, a detection event at D1a or D1b arises indistinguishably from either field 1L or 1R, so that the 
ensembles are projected into an entangled state, which in the ideal case can be written as: 
RL
i
RRLLRL
e 1001 1,
ηεε ±=Ψ   
where is the state with all atoms in the initial ground state,                                                               is 
the state with  one collective atomic excitation,  and εL (εR) is the normalized amplitude of photon generation from 
ensemble L(R). The phase η1 is determined by the difference of propagation phases from BSw to the ensembles and 
from the ensembles to BS1, for the write pulses and the fields 1L and 1R, respectively.  For the verification of the 
entangled state, η1 must be constant from trial to trial. In our experiment, it is actively stabilized using an auxiliary 
RL
R
NiL
gsg
1
......11 ∑= LNi
RL
R N ,
,
1
,
, =i
N
iRL
gRL ,1,0 =⊗=
       a1049_1.pdf        
       JTuA1.pdf
    
1-55752-813-6/06/$25.00 ©2006 IEEE
field at 1064 nm. 
 
 
 
 
 
 
 
 
 
 
Fig. 1. Schematic of the experiment. (a) entanglement preparation.  (b) entanglement detection. We use cesium atoms cooled and trapped in two 
independent magneto-optical traps at locations L and R. 
To verify entanglement, we map the delocalized atomic excitation into a field state (field 2), by applying 
simultaneously a read pulse to the ensembles (Fig 1b).  Since this operation is local, it cannot increase entanglement. 
The presence of entanglement in the field state is thus a signature of entanglement in the atomic ensembles.  The 
entanglement between the fields 2L and 2R is determined by a quantum tomography method, which takes into account 
various intrinsic and experimental imperfections of the measurement. We consider the following density matrix: 
⎟⎟
⎟⎟
⎟
⎠
⎞
⎜⎜
⎜⎜
⎜
⎝
⎛
=
11
01
*
10
00
2,2
000
00
00
000
p
pd
dp
p
RL
ρ  
where the pij  are the probabilities to find i photons in mode L and j photons in mode R, and d is the coherence between 
the |12L,02R> and |02L,12R> states.  To measure the diagonal elements, we send the two modes 2L and 2R directly to 
single photon detectors, in order to reconstruct the photon statistics. The coherence term d is measured by combining 
the two modes at a beam splitter BS2, and by applying a phase shift to one of the modes. An interference fringe is 
observed in the conditional counts with a visibility of ~70 %.  A lower bound of the entanglement can be determined 
by calculating the concurrence C given by with                                      PppdC ~/)0,22max( 1100−= 11011000~ ppppP +++=
We find: C(1a) = (2.4 ±0.6) ×10-3 > 0 and C(1b) = (1.9 ±0.6) ×10-3 > 0 for the states conditioned on a detection at D1a or 
D1b, respectively.  This conclusively demonstrates the presence of entanglement in the fields 2, and hence in the atomic 
ensembles.  The small value for the concurrence seems to be primarily due to the low atoms-light transfer efficiency (~ 
10 %). This efficiency can be in principle close to unity.  
Our work provides the first example of a stored atomic entanglement that can be transferred to propagating light 
fields, and significantly extends laboratory capabilities for entanglement generation, with now entangled “qubits” of 
matter stored with separation several thousand times larger than was previously possible. Although the entanglement 
creation is probabilistic, the initial detection heralds unambiguously the creation of an entangled state between the two 
ensembles, which can be stored and is physically available for subsequent utilization.  
 
[1] L.-M. Duan, M. D. Lukin, J. I. Cirac, P. Zoller, Nature 414, 413–418(2001) 
[2] C.W. Chou, H.de Riedmatten, D.Felinto. S.V.Polyakov, S.J.van Enk and  H.J.Kimble,  Nature 438, 828-832(2005) 
       a1049_1.pdf        
       JTuA1.pdf
    


Measurement induced entanglement for excitation stored in remote atomic ensembles

Crossref

Measurement-induced entanglement for excitation stored in remote atomic ensembles

A critical requirement for diverse applications in quantum information science is the capability to disseminate quantum resources over complex quantum networks. For example, the coherent distribution of entangled quantum states together with quantum memory (for storing the states) can enable scalable architectures for quantum computation, communication and metrology. Here we report observations of entanglement between two atomic ensembles located in distinct, spatially separated set-ups. Quantum interference in the detection of a photon emitted by one of the samples projects the otherwise independent ensembles into an entangled state with one joint excitation stored remotely in 10^5 atoms at each site. After a programmable delay, we confirm entanglement by mapping the state of the atoms to optical fields and measuring mutual coherences and photon statistics for these fields. We thereby determine a quantitative lower bound for the entanglement of the joint state of the ensembles. Our observations represent significant progress in the ability to distribute and store entangled quantum states

C.W Chou

S.V. Polyakov

S.J. van Enk

H.J. Kimble

https://authors.library.caltech.edu/93399/1/04628575.pdf

Measurement-Induced Entanglement for Excitation Stored in Remote Atomic
  Ensembles

Measurement-Induced Entanglement for Excitation Stored in Remote Atomic Ensembles

Abstract

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