Room-Temperature Quantum Memory for Polarization StatesThomas Mittiga, Connor Kupchak, Bertus Jordaan, Mehdi Namazi, Christian Noelleke, Eden Figueroa
Department of Physics and Astronomy, Stony Brook University, Stony Brook, NY 11794-3800, USA
Future perspectives: Storage of entanglement
Motivation • Practical implementation of a quantum memory is fundamental to realizing other quantum technologies.
• Quantum functionality has only been proven using cold-atom and cyrogenically cooled systems. Such systems are resource-intensive.
• Scalable Quantum Technology could benefit from room-temperature, easy-to-operate systems.
1) Write a probe photon using Electromagnetically-Induced Transparency.
Room-Temperature Operation
Introduction Quantum Memory Operation
Entangledsource
Bellmeasurement
Entangledsource
memory memory
entangled
• Even with filtering, physical processes generatebackground-photons at the same frequency.
Experimental Setup
S P C M
Etalon 2λ/4
BD BD
Etalon 1 λ/2 λ/4
FR
λ/2H-polarizer
State Reconstruction Filtering - control/probe suppression ratio: 130dB
λ/2
BDDiode laser
λ/2 λ/4BD GLP
87Rb-cellλ/2 λ/4
GLP BD
Attenuators
EIT Memory
Polarization Preparation
<n> polarized photonsmeasured before BD
L
M
Background Analysis
0 20 40 60 80 1000
0.02
0.04
0.06
Coun
ts/ p
ulse
Retrieval control eld power (mW)0 20 40 60 80 100
0
0.05
0.1
0.15St
orag
e e
cien
cy
0 20 40 60 80 1000
1
2
3
SBR
SBRη
ROI
Retrieval control eld power (mW)
The background may have three components: 1) Control field leakage through the filtering (technical noise, Red Dots). 2) Four-Wave Mixing (FWM). 3) Spontaneous emission.
Green Dots: Total background detected (all components).Purple Dots: Background minus leakage.Red Line: Fitting of a function . 6.835 GHz
Backgroundphoton
arXiv:1304.2264.The good t to the data indicates that FWMis the primary process preventing optimal
SBR at the optimal eciency.
∝√POWERΩC
0 1 2 3 4 5 6 70
1000
2000
3000
4000
Time (µs)
Inte
grat
ed c
ount
s
5000Storage signalBackground signal
A Quantum Technology‘s mass reproducibilityis key to its large-scale employment.
<n>= 6SBR = 0.84Expected Single-Photon SBR = 0.14
5 S21/2
5 P21/2
795nm
F=2
F=1
F=2
F=1
Δ
815MHz
6.834GHz
100MHz
Rb D1-Line @ 795nm87
Storage at the single-photon level
0 1 2 3 4 5 6 70
1000
2000
3000
4000
Time (µs)
Inte
grat
ed c
ount
s
Storage signalBackground signalAbsorbed probe (with Cell)Transmitted probe (No Cell)
ROI:Signal
ROI:Background
Storage experiments:• Probe pulse: <n>=1.6, 1μs long• SBR obtained by comparing counts in the ROI displayed; Efficiency by comparing the signal ROI to the transmitted probe.
EIT Configuration using
3) Retrieve
2) Map polsrization qubits onto a collective atomic excitation.
BDBDHWP HWP
ControlRb Vapor Cell
AOM
Controlfield
Quantum State
PPKTP
BBO
Diode Laser
Diode Laser
Diode Laser
6.8 GHz Phase Lock
1.2
GH
z ph
ase
lock
tuned to Rubidium1:1 transition
off atomic resonancebut in resonance withcavity
storedquantumstate
Remaining Issues:• Further noise-reduction • Cascade multiple memories• Store with lowest possible photon bandwidth
• This technique requires colinear fields, which presents the challenge of filtering 10 control photons.
Bottleneck: Low signal to background ratio
AOM: Acusto-optical modulators; BD: Beam displacers; GLP: Glan-Laser-Polarizer; FR: Faraday rotator; SPCM: Single-Photon-Counting-Module; L: Lens; M: Mirror. Probe: red beam paths; control: yellow beam paths
12
Fidelity Scaling with SBR
AV
<n>=1.1
<n>=16
<n>=2.1
<n>=2.7
<n>=4.0
<n>=5.5
<n>=6.8
<n>9.4
<n>=11.1
<n>=13.6
0 2 4 6 8 100.5
0.6
0.7
0.8
0.9
1
SBR
Fide
lity A
V
Green Dots: Fidelity between transmitted unstored and input statesBlue Dots: Fidelity between stored states and input statesRed Line: The result of the theortetical model with experimentally-measured values η = 0.055 and q = 0.005
The scaling of fidelity with SBR can be understood by a theoretical model considering a dual-rail memory and assuming each rail is a Poissonian source of uncorrelated signal and background photons:
,
where n and m are the number of photons produced, and p and q are the averages of the distributions.The probabilities of detection are:
So the Fidelity is
Storage of Polarization Qubits
Poincaré Sphere:(Left) transmitted input state (bold colors) and rotatedinput states (light colors).(Right) stored and retrieved output.
0
50
100
150
Time (µs)
A η=3.8%R η=5.6% L η=5.9%
H η=7.9% V η=5.3%D η=4.6%
Background
0 1 2 3 4 5 6 7
<n>=1.6
Stokes vectors reconstructed for each polarization:S and S are input and output vectors used to calculate Fidelity
in out
Input H V D A R L Average SBR 1.68 1.1 1.27 1.15 1.53 1.38 1.35±0.9
Fidelity (%) 71.3 79 69.2 71.4 70.2 67.6 71.5±1.6 Efficiency (η)(%) 7.9 5.3 4.6 3.8 5.6 5.9 5.5±0.6
arXiv:1405.6117
arXiv:1405.6117
arXiv:1405.6117
arXiv:1405.6117
