"Research and development towards commercial applications of quantum cryptography in non-entanglement and entanglement based systems" under the Action 1.4 of the Operational Programme for Innovative Economy of the Polish National Cohesion Strategy (supported

by the Polish Agency of Enteprise Development PARP and National Research and Development Center of Poland NCBiR)

Wroclaw Quantum Network – QKD deployment in a metropolitan networkM. Jacak2, T. Martynkien1, A. Janutka1, J. Jacak1, D. Melniczuk1, W. Donderowicz3, J. Gruber2, I. Jóźwiak2

1 Institute of Physics, Wrocław University of Technology, Wyb. Wyspiańskiego 27, 50-370 Wrocław, Poland2 Institute of Informatics, Wrocław Univeristy of Technology, Wyb. Wyspiańskiego 27, 50-370 Wrocław, Poland

3 CompSecur sp. z o.o. R&D Department, ul. Piłsudskiego 74/309, 50-020 Wrocław, Poland

Wrocław

REPUBLIC OF POLAND

City WrocławCountry - PolandVoivodeship - Lower SilesianPopulation (2012) - 631 188Area - 292.92 km2

Main river - Odra

Due to significant investments in Wrocław University of Technology laboratory equipment encom-passing current state-of-the-art quantum cryptography technolo-gies within the Polish National Quantum Technologies Laborato-

ry NLTK network programme, as well as technological partnerships with inter-nationally leading vendors of quantum cryptographic systems and national in-formation security institutions and companies, city of Wroclaw now hosts a unique metropolitan quantum network research and development project.

Experimental and even early commercial QKD implementations are very susceptible to technical conditionings of the transmitting media (i.e. optical fiber infrastructure and associated alignment of the quantum optics) therefore deployment of QKD systems in real metropolitan optical fiber infrastructure network poses a challenge

National Quantum Technologies Laboratory NLTK, Wrocław University of Technology

The optical infrastructure is determined by the city telecommunication canalization layout. Dark fibers connecting two, even not very distant metropolitan locations physically sharing an indus-try-standard telecom line with many parallel fibers (constituting the initial P2P topology and medium for QKD network) are divided in a series of thermally welded interconnections and junctions at tele-com canalization crossings, which are main reason for decoherence and quantum signal losses, re-sulting with increased QBER and with infeasibility of key distribution in practical scenarios (this is specifically addressed to dark fiber infrastructure of metropolitan backbone telecom networks with multiple interconnections of telecommunication optical lines, which are implemented by thermal weldings – a connection between two locations separated by ca. 4-5 km distance, is usually divided by even several fiber weldings)

RAW_KEY_EXCHANGE_RATE [bit/sec] dispersion in different QKD sequencesRAW_KEY_EXCHANGE_RATE [bit/sec] = 11143,0668-1,879*x

-50 0 50 100 150 200 250 300

QKD sequence no.

6000

7000

8000

9000

10000

11000

12000

RAW

_KE

Y_E

XC

HA

NG

E_R

ATE

[bit/

sec]

PRIVACY_AMPLIFICATION_QBER [#] dispersion in different QKD sequences

PRIVACY_AMPLIFICATION_QBER [#] = 0,0097-1,2974E-6*x

-50 0 50 100 150 200 250 300QKD sequence no.

0,008

0,009

0,010

0,011

0,012

0,013

0,014

0,015

0,016

PR

IVA

CY

_AM

PLI

FIC

ATIO

N_Q

BE

R [#

]

DISTILLATION_SECRET_BITS [bit] dispersion in different QKD sequences

DISTILLATION_SECRET_BITS [bit] = 5,9665E5-57,2637*x

-50 0 50 100 150 200 250 300QKD sequence no.

1,5E5

2E5

2,5E5

3E5

3,5E5

4E5

4,5E5

5E5

5,5E5

6E5

6,5E5

DIS

TILL

ATIO

N_S

EC

RE

T_B

ITS

[bit]

X and MR Control charts: PRIVACY_AMPLIFICATION_QBER [#]

X: ,00949 (,00949); Sigma: ,14E-3 (,14E-3); n: 1,

50 100 150 200 2500,0080,0090,0100,0110,0120,0130,0140,0150,016

,00908,00949,00990

normality chart

0,0080,009

0,0100,011

0,0120,013

0,0140,015

0,016-4

-2

0

2

4

0.010.050.150.300.500.700.850.950.99

moving R: ,15E-3 (,15E-3); Sigma: ,12E-3 (,12E-3); n: 1,

50 100 150 200 250-0,0010,0000,0010,0020,0030,0040,0050,0060,007

0,0000,15E-3,51E-3

capacity chart

0,00750,0080

0,00850,0090

0,00950,0100

0,01050,0110

0,0115

spec.total

sampling

individual observations chart

X: ,00949 (,00949); Sigma: ,14E-3 (,14E-3); n: 1,

50 100 150 200 2500,0080,0100,0120,0140,016

,00908,00949,00990

capacity, histogram

0,00

760,

0078

0,00

800,

0082

0,00

840,

0086

0,00

880,

0090

0,00

920,

0094

0,00

960,

0098

0,01

000,

0102

0,01

040,

0106

0,01

080,

0110

0,01

120,

0114

-3,*SLSLnominal value

USL+3,*S

0

40

80

sampling SD: ,1E-3; Cp: 1,185; Cpk: 1,185

total SD: ,5E-3; Pp: ,3333; Ppk: ,3333

LSL: ,0090; Nom.: ,0095; USL: ,0100

X and moving R chart; variable: RAW_KEY_EXCHANGE_RATE [bit/sec]

observation histogram

020

4060

80100

120140

160180

20060006500700075008000850090009500

1000010500110001150012000

X: 10885, (10885,); Sigma: 50,122 (50,122); n: 1,

50 100 150 200 250

10734,10885,11035,

moving range histogram

050

100150

200250

300-500

0500

1000150020002500300035004000450050005500

moving R: 56,556 (56,556); Sigma: 42,729 (42,729); n: 1,

50 100 150 200 250

0,000056,556184,74

Sample characteristics of entanglement based QKD deployment setup:

Quantum optics and electronic components assembled in an integrated R&D system perform-ing quantum key distribution (QKD) by means of quantum entanglement:

Quantum opto-electronic setups generating quantum entanglement in photons polariza-tions, integrated within 2 end-stations in both optical fibres (WDM compatibility) and tele-scopic (free laser beam) configurations, computer controlled with a hardware/software architectureFeaturing non-linear crystal implementation of the parametric down conversion procedure of quantum entanglement production in photon polarizations states (carrier of the informa-tion implemented on the polarization of photons in quantum entangled states)Including laser photon source and avalanche photodiode detectors (temperature stabilized)Featuring implementation of entanglement based QKD protocol (including implementation of key sifting, key distillation, error correction and privacy amplification functional layers)Featuring integrated electronic control and interface systems (including synchronization systems)Including software suite (containing programming libraries)QKD distance: at least 5 kmKeyrate: at least 0,2 Kbit/s on a 5 km distanceTemperature of operation between 10 and 30 °C

The entanglement based QKD has been tested for the first time in a real telecom network environment and proved to be also feasible but within a very narrow gap of optical elements alignment and im-practically poor values of QBER and RKER with additional high in-stability of operation parameters. Results of the presented laborato-ry research were analyzed within X-R Shewhart control charts of RKER and QBER and proved as feasible deployment of the QKD metropolitan network in Wroclaw, which is currently taking place.

Statistical analysis: dispersion of RKER, QBER and BSD based on 274 quantum key distribution sequences

Sample characteristics of non-entanglement QKD deployment setup:

Quantum optics and electronic components assembled in an integrated R&D system performing quantum key distribution (QKD) without using of quantum entanglement:

Quantum opto-electronic setups integrated within 2 end-stations connected by optical fibres (WDM compatibili-ty) and computer controlled with a hardware/software archi-tectureIncluding laser photon source and avalanche photodiode detectors (temperature stabilized)Featuring photon phase qubit coding (interferometers with auto-compensation)Featuring implementation of BB84, B92, SARG04 QKD protocolsIncluding software suite (containing programming libraries)QKD distance: at least 50 kmKeyrate: at least 1 Kbit/s on a 25 km distanceTemperature of operation between 10 and 30 °C

Measurements were performed for different number of fiber interconnections, different fiber types and different weldings number in quantum channel between Alice and Bob stations [7 km fiber spool SMF28 with F3000/APC, telecom standard single-mode optical dark fiber line of ca. 4.8 km and 4 up to 14 weldings (thermal optical fiber weldings), few 1-meter SMF28 fiber segments with F3000/APC and FC/PC connectors, few 2-meter SMF28 fiber segments with FC/PC connectors (inter-connected via FC/PC symmetric adapters)]

Research on QKD deployment in practical telecommunication network environments resulted in evaluation of boundary conditions for QKD feasibility versus quantum channel and transmission parameters and a success-ful resolution of channel quality problem by proper alignment of experimental QKD setups. The fiber optics line of the SMF28 standard has been used to test different connection and welding configurations for two R&D QKD approaches based on the IdQuantique Clavis2 setup (non-entanglement QKD, encoding qubits on inter-fering phase shifts of laser impulses in Mach-Zehnder interferometers) and the AIT Quelle setup (entangle-ment QKD, encoding qubits on polarizations of entangled photon pairs generated in non-linear PDC process in a BBO crystal). The main optics fiber line (single mode SMF28 standard) has been subsequently modified in laboratory test runs by welded or interconnected F3000/APC and FC/PC adapters. The interconnectors re-sulted with high QBER increases, thus favoring thermal welding which in proper proximity distribution were characterized by ca. 10 times lower loss induction than interconnectors (ca. 0.01 dB per welding, depending on the proximities). Next the industry standard telecom fiber optics line tests have been carried out towards welding and interconnections configuration optimizing in regard to QBER and conditioning of the metropolitan network deployment. Primary focus was directed towards the non-entanglement based setup which turned out to be operating properly with an acceptable raw key exchange rate (RKER) generating targeted amount of dis-tilled secret bits (DSB) under laboratory simulation of real optic fiber backbone metropolitan network configura-tion with required optimization of interconnections and welding infrastructure. The entanglement based QKD has been tested for the first time in a real telecom network environment and proved to be also feasible but within a very narrow gap of optical elements alignment and poor (unpractical) values of QBER and RKER with high additional instability of operation parameters. This research allowed for the current deployment of the QKD metropolitan network in Wroclaw.

•

•

•

•

•

••••

•

•

•

••

•

••••

Categorized histogramVariable: PRIVACY_AMPLIFICATION_QBER [#] conn1+_conn3+_conn5+_conn6+_conn7+

obse

rvat

ions

cou

nt

group: conn1+

0,00

60,

007

0,00

80,

009

0,01

00,

011

0,01

20,

013

0,01

40,

015

0,01

60,

017

0,01

8

0

40

80

120

160

200

240

280

group: conn3+

0,00

60,

007

0,00

80,

009

0,01

00,

011

0,01

20,

013

0,01

40,

015

0,01

60,

017

0,01

8

group: conn5+

0,00

60,

007

0,00

80,

009

0,01

00,

011

0,01

20,

013

0,01

40,

015

0,01

60,

017

0,01

8

group: conn6+

0,00

60,

007

0,00

80,

009

0,01

00,

011

0,01

20,

013

0,01

40,

015

0,01

60,

017

0,01

8

0

40

80

120

160

200

240

280

group: conn7+

0,00

60,

007

0,00

80,

009

0,01

00,

011

0,01

20,

013

0,01

40,

015

0,01

60,

017

0,01

8

Range plot RKER , Sigma_RKER , Sigma_RKER

connectors number

1 2 3 4 5 6 78500

9000

9500

10000

10500

11000

11500

12000

12500

Range plot QBER , Sigma_QBER , Sigma_QBER

connectors number

1 2 3 4 5 6 70,007

0,008

0,009

0,010

0,011

0,012

0,013

0,014

day 1 day 2 day 3 day 4

0.015

0.020

0.025

0.030

0.035

0.040

0.045

day 1 day 2 day 3 day 4

0.012

0.014

0.016

0.018

0.020

0.022

Privacy amplification QBER+7 conn. +5 conn. +3 conn. +1 conn. +2 conn. +4 conn.

day 1 day 2 day 3 day 45000

6000

7000

8000

9000

10000

11000

12000

Raw key exchange rate+7 conn. +5 conn. +3 conn. +1 conn. +2 conn. +4 conn.

Statistical analysis points that QBER distribution character seems not to be universal (for both systems - non-entanglement and entanglement based)Important issue of lack of repeatability of systems parameter measurements (for statistical analysis) - strong influence of external factors (e.g. temperature). It is difficult to observe steady work character of systems. Different passes on the same quantum channel can result with quite different results. Possible problems with end terminals synchronization can have some influence on meas-urement data.Observed characteristics seems to present discrete step changes of parameters - inter alia due to procedures of self-diagnostics/recalibration of systems but also due to unpredicted reactions to external factors.Observed QBER value, despite the difficulties resulting from unpredictable system behav-ior, show expected raise with the increase of connectors (introducing higher disturbance) and weldings (introduction lower disturbance) number.Tested systems seems to maintain efficiency only up to ca. 5 km in case of a real telecom commercial fiber

•

•

•

•

•

•

123

1

2

3

1km

5km