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