Long-term transmission of entangled photons from single quantum dot over deployed fiber
Zi-Heng Xiang Jan Huwer R. Mark Stevenson Joanna Skiba-Szymanska Martin B. Ward Ian Farrer David A. Ritchie Andrew J. Shields





Toshiba Research Europe Limited, Cambridge Research Laboratory, 208 Science Park, Milton Road, Cambridge, CB4 0GZ, UK.
Cavendish Laboratory, JJ Thomson Ave, Cambridge, CB3 0HD, UK.

jan.huwer@crl.toshiba.co.uk
Toshiba Research Europe Limited, Cambridge Research Laboratory, 208 Science Park, Milton Road, Cambridge, CB4 0GZ, UK.

Toshiba Research Europe Limited, Cambridge Research Laboratory, 208 Science Park, Milton Road, Cambridge, CB4 0GZ, UK.

Toshiba Research Europe Limited, Cambridge Research Laboratory, 208 Science Park, Milton Road, Cambridge, CB4 0GZ, UK.

Toshiba Research Europe Limited, Cambridge Research Laboratory, 208 Science Park, Milton Road, Cambridge, CB4 0GZ, UK.

Cavendish Laboratory, JJ Thomson Ave, Cambridge, CB3 0HD, UK.
Present Address: Department of Electronic & Electrical Engineering, University of Sheffield, Sheffield S1 3JD, UK.

Cavendish Laboratory, JJ Thomson Ave, Cambridge, CB3 0HD, UK.
Toshiba Research Europe Limited, Cambridge Research Laboratory, 208 Science Park, Milton Road, Cambridge, CB4 0GZ, UK.

Toshiba Research Europe Limited, Cambridge Research Laboratory, 208 Science Park, Milton Road, Cambridge, CB4 0GZ, UK.




Non-classical light sources based on a single quantum emitter are considered as core technology for multiple quantum network architectures. A large variety of sources has been developed, but the generated photons remained far from being utilized in established standard fiber networks.
Here, we report a week-long transmission of polarization-entangled photons from a single InAs/GaAs quantum dot over a metropolitan network fiber. The emitted photons are in the telecommunication O-band, favored for fiber optical communication. We employ a polarization stabilization system overcoming changes of birefringence introduced by 18.23km of installed fiber. Stable transmission of polarization-encoded entanglement with a high fidelity of 91% is achieved, facilitating the operation of sub-Poissonian quantum light sources over existing fiber networks.



Long-term transmission of entangled photons from single quantum dot over deployed fiber
    Andrew J. Shields
    December 30, 2023
=======================================================================================




With the number of emerging quantum technologies rapidly increasing, the development of quantum networks is becoming more important than ever. Apart from special purpose networks suitable for secure key distribution <cit.>, more general architectures like a quantum internet<cit.> are expected to unlock even greater potential for applications like cloud-based quantum computing <cit.> or quantum sensing <cit.>. Apart from many other challenges, the most basic discipline in a general purpose quantum network is the generation and detection of entangled quantum bits (qubits). For true scalability not only in distance but also for widespread implementation, approaches are required that enable these two essential tasks in the most simple and robust way. 



Since the early days, photon pair sources based on spontaneous processes like down conversion <cit.> and more recently four-wave mixing <cit.> were the most prominent choice for photonic entanglement generation. Over the years, the technology has evolved, enabling a large number of quantum-network related experiments. But due to their spontaneous nature, these sources can increase error rates in certain security-relevant applications caused by multi-pair emission <cit.>. Sub-Poissonian photon pair sources based on a single quantum emitter such as semiconductor quantum dots (QD) are a promising alternative, as they provide intrinsic security against photon number splitting attacks.

Regarding photonic qubits, there exist two competing approaches for their implementation over optical fiber. Quantum states being encoded in the photon polarization are naturally favored for qubit generation in sources being based on single quantum emitters <cit.>, as they can directly interface with electronic states on optical dipole transitions. However, for long-distance transmission over optical fiber, polarization qubits are affected by random drifts in birefringence due to changing environmental conditions. In contrast, qubits encoded in the phase of subsequent time-bins are realized in a single polarization basis, protecting their information from birefringence-induced rotations and enabling simple stabilization schemes <cit.>. The major disadvantage is that stable interferometers are required for generation and detection, significantly increasing the complexity of the systems.

For certain scenarios, where multiple users are sharing the same quantum channel, the use of polarization encoding might be beneficial. The network provider could take care of the stabilization of birefringence, allowing the end user to operate with cheaper and less sensitive technology, important for scalable and wide-spread implementation. A number of experiments have been performed in the past, employing the transmission of polarization qubits over short specially installed non-telecom fiber without <cit.> and with <cit.> active stabilization. Efficient feedback systems for the continuous recovery of arbitrary polarization states operating at telecom wavelength have been demonstrated, enabling the stable transmission of polarization qubits from weak coherent sources over long fiber in a laboratory <cit.> and from a down-conversion source over deployed fiber  <cit.>. Here, we implement a similar polarization-control system to stabilize birefringence in 18km of installed fiber across the city of Cambridge. We make use of a telecom-wavelength semiconductor quantum dot as photon source and show stable long-term operation of polarization-entangled photon transmission from a sub-Poissonian emitter over a standard telecommunication-fiber network link.

 

In recent years, effort has been put to push the emission wavelength of QDs to the standard telecommunication bands, enabling sub-Poissonian entangled photon-pair sources compatible with standard telecommunication infrastructure <cit.>. The InAs/GaAs quantum dot used in this work is located in a PIN structure grown by molecular beam epitaxy with AlGaAs/GaAs stacked Bragg mirrors at the P type and N type layer in order to enhance photon collection <cit.>. The ground state of a QD can be occupied with a maximum of two electron-hole pairs which decay in a cascade from the so-called biexciton level (XX) via the intermediate exciton level (X). The two subsequently emitted photons are maximally entangled in their polarization <cit.> corresponding to the Bell state |Φ^+⟩ = 1/√(2) (|H_XH_XX⟩ + |V_XV_XX⟩) with H and V denoting horizontal and vertical polarization respectively. A continuous wave laser at 1064nm is used to optically excite the quantum dot at a temperature of 10K. We apply a bias of -0.165V to the diode, tuning the emission wavelength of XX photons to 1320.0nm and X photons to 1329.4nm.

Figure <ref> illustrates the overall experimental setup. Polarization entangled photon pairs in the telecom O-band are generated from the quantum dot in (a). The light emitted from the device is coupled to single-mode fiber using a confocal microscope configuration, and passes through a free-space spectral filter to isolate entangled qubits into two separate single modes. One photon of a pair is transmitted over short optical fiber to a polarization analyzing setup directly in the lab, whereas the partner photon is sent over a loop-back fiber to the city center of Cambridge before detection back in the laboratory (b). Boxes (c) and (d) display the setup required for polarization stabilization over the deployed fiber.

The main difficulty in transmitting qubits encoded in polarization is to overcome polarization rotations induced by temporal variations of birefringence in installed fibers. The general approach is to inject polarization references which enable efficient detection and compensation of these variations when applying feedback to a set of polarization controllers. Over the network fiber, we observe a strong wavelength dependence of birefringence <cit.>. This results in a change of polarization states of 20 degrees on average on the Poincaré sphere for small variations in wavelength of 1nm. Changes in environmental conditions cause a continuous variation of the birefringence <cit.>, resulting in polarization states of different wavelength evolving in a different random way. Therefore, wavelength-division multiplexing schemes <cit.> could not be implemented for injection and retrieval of the references. We thus apply a time-division multiplexing scheme <cit.>, with both references and the quantum light at exactly the same wavelength.

For generation of the two references in Figure <ref>(c) we split polarized laser light at 1320nm in two separate spatial modes and use a free-space quarter wave plate (QWP) in one mode for a precise and long-term stable alignment of both polarizations along two orthogonal directions on the Poincaré sphere. In this configuration, the stabilization of both references efficiently locks arbitrary rotations of the sphere. An optical switch (OSW 1) is used to select either one of the two references. Two standard power meters in (d) are used to evaluate the projection η along the corresponding bases on the  Poincaré sphere, controlled by electronic polarization controllers (EPC) 3 and 4 and polarizing beam splitter (PBS) 3:

    η = (P_1- P_2)/(P_1+P_2)

where P_1 and P_2 denote the power values measured by each power meter. OSW 2 and 3 are used for fast and reliable switching between the two detection bases. Once a drop in η is detected for one of the references, EPC 5 and a fiber variable wave plate (FWP) in the purple box are used for applying rotations such that both references are recovered to their original state. Applying a voltage to the FWP results in a clean variable rotation of polarization states around a fixed axis on the Poincaré sphere. EPC 3 and 4 are set such that one detection basis coincides with the rotation axis of the FWP and the other one is oriented in plane of the rotation. Like this, cross-talk during the recovery of the references is minimized. Both, EPC 5 and FWP are all-fiber based standard components featuring low insertion loss(< 0.8dB) and low-voltage operation.



Photon entanglement is analysed by processing time-resolved correlations c_MN between measured X and XX photon arrival times for co- and cross-polarized states M and N in the three detection bases HV, DA (diagonal, anti-diagonal) and RL (right-, left-circular). These bases are initially calibrated using EPC 1 and 2 after injecting polarization references at the position of the QD, not displayed in Figure <ref>. The fidelity to the maximally entangled Bell  |Φ^+⟩ state is calculated as <cit.>

    F =  ( 1+C_HV+C_DA-C_RL)/4

with C_MN = (c_MM-c_MN)/(c_MM+c_MN) being the correlation contrast. Both, source and superconducting single photon detectors are running continuously during the measurements. The detection basis is switched every 10 min such that the fidelity can be evaluated for every 30 min of correlation data. An example for one set of data is shown in Figure <ref> (b). Due to imperfections in the QD morphology, the fidelity follows a time-dependent oscillation caused by interference of two non-degenerate decay channels in the cascade introduced by the so-called fine structure splitting <cit.>. In order to extract the entanglement fidelity to  |Φ^+⟩, a post selection window is applied to each data set, isolating  correlations in a 48ps interval around the zero delay of the cascade. As changes in the ambient temperature result in a change of the effective optical length of the installed fiber, an exact knowledge of the zero delay is crucial in this analysis. As both photons of a pair are detected by the same single photon counting unit, no active synchronization is required. We extract the time-of flight for each 30min chunk of data from a fit to correlations c_HH between X and XX photons measured in the HV polarization basis (Figure  <ref> (a)). Over this time scale the drift is typically negligible. The overall timing jitter of the photon detection system is 70ps and correlation data is analyzed on a 48ps timing grid.

The entanglement fidelity has been continuously recorded for 7 days, with the XX photons being sent over the field fiber. The overall results are shown in Figure <ref>. Displayed is the entanglement fidelity and the change in time-of-flight as a function of measurement time. A constantly high entanglement fidelity is achieved over the entire week, with an average value of  (91.3 ± 1.4)%. For comparison, the entanglement fidelity measured without sending the photons over the loop-back link is  (94.7 ± 1.7)%. During the course of the week, rain has dropped and snow has fallen over Cambridge, with the temperature variation from -4 to 7 °C. The impact of these changing environmental conditions can be seen in the drift of the time-of-flight of photons of 1.82ns over the first 4 days. Figure <ref> shows the voltages applied to the four channels of the EPC and the FWP as a result of the feedback generated to keep the birefringence stable. Superimposed to the steady drift over the first 4 days, one can see clear oscillations in EPC and FWP operation voltages corresponding to the day-night cycle of temperatures.



When using time-division multiplexing schemes, it is essential to achieve high duty cycles for qubit transmission. Over the course of the measurement, the polarization references were checked for 0.5s alternatingly every 60s, corresponding to a duty cycle of 99%. Once the projection value η dropped below a threshold of 98.5%, feedback for recovery was applied which took around 5s on average, resulting in a duty cycle of 92%. Apart from the threshold-based check, the recovery system was activated every 11 minutes to maximize the alignment for both references. Thus, an overall duty cycle of 98% with polarization maintenance over 98.5% was realized for the qubit transmission. Since the optical switches used for multiplexing allow for switching speeds above 100Hz it will be straight forward to adopt the system to field fibers experiencing much higher drift rates than the link available for this work.

Quantum light sources based on single quantum emitters are one of the most precious resources in a quantum network. As the brightness of these sources cannot be easily tuned like attenuated lasers, it is crucial that independent feedback systems add as little loss as possible. With this in mind, the system has been designed using standard fiber components with low insertion loss. The combined losses of optical switches OSW 4 and 5 used for multiplexing between quantum signal and references, and EPC 5 and FWP used for stabilization, add up to 3.49dB, which can be further reduced by splicing. The installed loop-back fiber has a total length of 18.23km and a measured loss of 11.70dB for the transmission of photons at 1320nm.

In summary, we have reported for the first time the long-term transmission of polarization qubits from a single quantum-dot emitter over 18.23km of installed standard telecom fiber. The transmitted photons exhibit a constantly high entanglement fidelity of 91.3% with their partner photons measured locally, corresponding to a drop in fidelity by only 3.4% with respect to the source properties. The system has a low systematic loss and a high duty cycle that allows a high transmission efficiency of the qubits. The results demonstrate that quantum-dot emitters natively operating at telecom wavelength, combined with the deployment of entangled qubits over installed fiber, provide a reliable and stable technology which is highly competitive in terms of its low level of complexity, regarding qubit generation and robust detection schemes.


The authors acknowledge partial financial support from the Engineering and Physical Sciences Research Council (EPSRC) and the EPSRC Quantum Technology Hubs in Quantum Communications. Z-H. Xiang acknowledges support from the Cambridge Trust and China Scholarship Council(CSC). The authors would like to thank J. Dynes for technical discussions and A. Wonfor for arrangement of the loop-back fiber link.


38
fxundefined [1]
 ifx#1

fnum [1]
 #1firstoftwo
 secondoftwo
 
fx [1]
 #1firstoftwo
 secondoftwo
 





noop [0]secondoftwo

ref[1]@startlink#1@href
href[1]#1@endlink
anitize@url [0]`
12`$12`&12`#12`1̂2`_12`%12
startlink[1]
endlink[0]

rl [1]href #1












@bib@innerbibempty

[Ekert(1991)]ekert1991quantum
  author author A. K. Ekert, @noop  journal journal
  Physical review letters volume 67, pages 661 (year 1991)NoStop
[Qiu et al.(2014)Qiu et al.]qiu2014quantum
  author author J. Qiu et al., @noop  journal journal Nature volume 508, pages
  441 (year 2014)NoStop
[Tajima et al.(2017)Tajima,
  Kondoh, Ochi, Fujiwara,
  Yoshino, Iizuka, Sakamoto,
  Tomita, Shimamura, Asami
  et al.]tajima2017quantum
  author author A. Tajima, author T. Kondoh,
  author T. Ochi, author
  M. Fujiwara, author
  K. Yoshino, author H. Iizuka, author T. Sakamoto, author A. Tomita, author E. Shimamura, author S. Asami,  et al., @noop  journal journal Quantum Science and Technology volume 2, pages 034003 (year
  2017)NoStop
[Sasaki et al.(2011)Sasaki,
  Fujiwara, Ishizuka, Klaus,
  Wakui, Takeoka, Miki,
  Yamashita, Wang, Tanaka et al.]sasaki2011field
  author author M. Sasaki, author M. Fujiwara,
  author H. Ishizuka, author W. Klaus, author
  K. Wakui, author M. Takeoka, author S. Miki, author T. Yamashita, author Z. Wang,
  author A. Tanaka,  et al., @noop  journal journal Optics
  express volume 19, pages 10387
  (year 2011)NoStop
[Kimble(2008)]kimble2008quantum
  author author H. J. Kimble, @noop  journal journal
  Nature volume 453, pages 1023
  (year 2008)NoStop
[Liao et al.(2018)Liao,
  Cai, Handsteiner, Liu,
  Yin, Zhang, Rauch,
  Fink, Ren, Liu et al.]liao2018satellite
  author author S.-K. Liao, author W.-Q. Cai,
  author J. Handsteiner, author B. Liu, author
  J. Yin, author L. Zhang, author D. Rauch, author M. Fink, author J.-G.  Ren, author W.-Y. Liu,  et al., @noop  journal journal Physical Review Letters volume 120,  pages 030501 (year 2018)NoStop
[Cirac et al.(1999)Cirac,
  Ekert, Huelga, and Macchiavello]cirac1999distributed
  author author J. Cirac, author A. Ekert,
  author S. Huelga,  and author C. Macchiavello, @noop 
  journal journal Physical Review A volume 59, pages 4249 (year
  1999)NoStop
[Lim, Beige, and Kwek(2005)]lim2005repeat
  author author Y. L. Lim, author A. Beige,  and  author L. C. Kwek, @noop
   journal journal Physical review letters  volume 95, pages 030505 (year 2005)NoStop
[Degen, Reinhard, and Cappellaro(2017)]degen2017quantum
  author author C. L. Degen, author F. Reinhard,   and author P. Cappellaro,  @noop  journal journal Reviews of modern
  physics volume 89, pages 035002
  (year 2017)NoStop
[Medintz et al.(2005)Medintz, Uyeda, Goldman, and  Mattoussi]medintz2005quantum
  author author I. L. Medintz, author H. T. Uyeda,
  author E. R. Goldman,  and  author H. Mattoussi, @noop
   journal journal Nature materials volume 4, pages 435 (year
  2005)NoStop
[Kwiat et al.(1995)Kwiat,
  Mattle, Weinfurter, Zeilinger, Sergienko, and Shih]kwiat1995new
  author author P. G. Kwiat, author K. Mattle,
  author H. Weinfurter, author A. Zeilinger, author
  A. V. Sergienko,  and author
  Y. Shih, @noop  journal journal Physical Review Letters volume 75, pages 4337 (year
  1995)NoStop
[Li et al.(2005)Li,
  Voss, Sharping, and Kumar]li2005optical
  author author X. Li, author P. L. Voss,
  author J. E. Sharping,  and  author P. Kumar, @noop 
  journal journal Physical review letters  volume 94, pages 053601 (year 2005)NoStop
[Gisin et al.(2002)Gisin,
  Ribordy, Tittel, and Zbinden]gisin2002quantum
  author author N. Gisin, author G. Ribordy,
  author W. Tittel,  and author H. Zbinden, @noop 
  journal journal Reviews of modern physics  volume 74, pages 145 (year
  2002)NoStop
[Benson et al.(2000)Benson,
  Santori, Pelton, and Yamamoto]benson2000regulated
  author author O. Benson, author C. Santori,
  author M. Pelton,  and author Y. Yamamoto, @noop 
  journal journal Physical review letters  volume 84, pages 2513 (year
  2000)NoStop
[Stevenson et al.(2006)Stevenson, Young, Atkinson, Cooper, Ritchie, and Shields]stevenson2006semiconductor
  author author R. M. Stevenson, author R. J. Young, author P. Atkinson,
  author K. Cooper, author D. A. Ritchie,  and author A. J. Shields, @noop 
  journal journal Nature volume 439, pages 179 (year
  2006)NoStop
[Moreau et al.(2001)Moreau,
  Robert, Gérard, Abram,
  Manin, and Thierry-Mieg]moreau2001single
  author author E. Moreau, author I. Robert,
  author J. Gérard, author I. Abram, author
  L. Manin,  and author
  V. Thierry-Mieg, @noop  journal journal Applied Physics Letters volume 79, pages 2865 (year
  2001)NoStop
[Wilk et al.(2007)Wilk,
  Webster, Kuhn, and Rempe]wilk2007single
  author author T. Wilk, author S. C. Webster,
  author A. Kuhn,  and author G. Rempe, @noop 
  journal journal Science volume 317, pages 488 (year
  2007)NoStop
[Babinec et al.(2010)Babinec, Hausmann, Khan, Zhang, Maze, Hemmer, and Lončar]babinec2010diamond
  author author T. M. Babinec, author B. J. Hausmann, author M. Khan,
  author Y. Zhang, author J. R. Maze, author
  P. R. Hemmer,  and author
  M. Lončar, @noop  journal journal Nature nanotechnology volume 5, pages 195 (year 2010)NoStop
[Marcikic et al.(2004)Marcikic, De Riedmatten, Tittel,
  Zbinden, Legré, and Gisin]marcikic2004distribution
  author author I. Marcikic, author H. De Riedmatten, author W. Tittel, author H. Zbinden,
  author M. Legré,  and  author N. Gisin, @noop 
  journal journal Physical Review Letters  volume 93, pages 180502 (year 2004)NoStop
[Yoshino et al.(2013)Yoshino, Ochi, Fujiwara, Sasaki, and Tajima]yoshino2013maintenance
  author author K.-i. Yoshino, author T. Ochi,
  author M. Fujiwara, author M. Sasaki,  and author
  A. Tajima, @noop  journal journal Optics express volume
  21, pages 31395 (year 2013)NoStop
[Dynes et al.(2016)Dynes,
  Tam, Plews, Fröhlich,
  Sharpe, Lucamarini, Yuan,
  Radig, Straw, Edwards et al.]dynes2016ultra
  author author J. F. Dynes, author W. W. Tam,
  author A. Plews, author B. Fröhlich, author
  A. W. Sharpe, author
  M. Lucamarini, author
  Z. Yuan, author C. Radig, author A. Straw, author T. Edwards,  et al., @noop  journal journal Scientific reports volume 6, pages 35149 (year
  2016)NoStop
[Dixon et al.(2015)Dixon,
  Dynes, Lucamarini, Fröhlich, Sharpe, Plews, Tam, Yuan, Tanizawa, Sato
  et al.]dixon2015high
  author author A. Dixon, author J. Dynes,
  author M. Lucamarini, author B. Fröhlich, author
  A. Sharpe, author A. Plews, author S. Tam, author Z. Yuan, author Y. Tanizawa,
  author H. Sato,  et al.,  @noop  journal journal Optics express  volume 23, pages 7583 (year
  2015)NoStop
[Ursin et al.(2004)Ursin,
  Jennewein, Aspelmeyer, Kaltenbaek, Lindenthal, Walther, and  Zeilinger]ursin2004communications
  author author R. Ursin, author T. Jennewein,
  author M. Aspelmeyer, author R. Kaltenbaek, author
  M. Lindenthal, author
  P. Walther,  and author
  A. Zeilinger, @noop  journal journal Nature volume 430,  pages 849 (year 2004)NoStop
[Rosenfeld et al.(2017)Rosenfeld, Burchardt, Garthoff,
  Redeker, Ortegel, Rau, and  Weinfurter]rosenfeld2017event
  author author W. Rosenfeld, author D. Burchardt, author R. Garthoff,
  author K. Redeker, author N. Ortegel, author
  M. Rau,  and author
  H. Weinfurter, @noop  journal journal Physical review letters volume 119, pages 010402 (year
  2017)NoStop
[Xavier et al.(2008)Xavier,
  de Faria, Temporão, and Von der Weid]xavier2008full
  author author G. Xavier, author G. V. de Faria, author G. Temporão,  and author J. Von der Weid, @noop  journal journal
  Optics express volume 16, pages 1867
  (year 2008)NoStop
[Peng et al.(2007)Peng,
  Zhang, Yang, Gao,
  Ma, Yin, Zeng, Yang, Wang, and Pan]peng2007experimental
  author author C.-Z. Peng, author J. Zhang,
  author D. Yang, author
  W.-B. Gao, author H.-X. Ma, author H. Yin, author H.-P.  Zeng, author T. Yang, author X.-B. Wang,   and author J.-W. Pan,  @noop  journal journal Physical review
  letters volume 98, pages 010505
  (year 2007)NoStop
[da Silva et al.(2013)da Silva, Vitoreti, Xavier, do Amaral, Temporao, and von der
  Weid]da2013proof
  author author T. F. da Silva, author D. Vitoreti,
  author G. Xavier, author G. do Amaral, author
  G. Temporao,  and author
  J. von der Weid, @noop  journal journal Physical Review A volume 88, pages 052303 (year
  2013)NoStop
[Treiber et al.(2009)Treiber, Poppe, Hentschel, Ferrini, Lorünser, Querasser,
  Matyus, Hübel, and Zeilinger]treiber2009fully
  author author A. Treiber, author A. Poppe,
  author M. Hentschel, author D. Ferrini, author
  T. Lorünser, author
  E. Querasser, author
  T. Matyus, author H. Hübel,  and author A. Zeilinger, @noop  journal
  journal New Journal of Physics volume
  11, pages 045013 (year 2009)NoStop
[Alloing et al.(2005)Alloing, Zinoni, Zwiller, Li, Monat, Gobet, Buchs,
  Fiore, Pelucchi, and Kapon]alloing2005growth
  author author B. Alloing, author C. Zinoni,
  author V. Zwiller, author L. Li, author
  C. Monat, author M. Gobet, author G. Buchs, author A. Fiore, author E. Pelucchi,  and author E. Kapon, @noop  journal journal Applied Physics Letters volume 86,  pages 101908 (year 2005)NoStop
[Benyoucef et al.(2013)Benyoucef, Yacob, Reithmaier, Kettler, and Michler]benyoucef2013telecom
  author author M. Benyoucef, author M. Yacob,
  author J. Reithmaier, author J. Kettler,  and author P. Michler, @noop 
  journal journal Applied Physics Letters  volume 103, pages 162101 (year 2013)NoStop
[Ward et al.(2005)Ward,
  Karimov, Unitt, Yuan,
  See, Gevaux, Shields,
  Atkinson, and Ritchie]ward2005demand
  author author M. Ward, author O. Karimov,
  author D. Unitt, author Z. Yuan, author
  P. See, author D. Gevaux, author A. Shields, author P. Atkinson,  and author D. Ritchie, @noop  journal journal Applied Physics Letters volume 86,  pages 201111 (year 2005)NoStop
[Skiba-Szymanska et al.(2017)Skiba-Szymanska, Stevenson, Varnava,
  Felle, Huwer, Müller,
  Bennett, Lee, Farrer,
  Krysa et al.]skiba2017universal
  author author J. Skiba-Szymanska, author R. M. Stevenson, author C. Varnava,
  author M. Felle, author J. Huwer, author
  T. Müller, author
  A. J. Bennett, author
  J. P. Lee, author I. Farrer, author A. B.  Krysa,  et al., @noop  journal
  journal Physical Review Applied volume
  8, pages 014013 (year 2017)NoStop
[Huwer et al.(2017)Huwer,
  Stevenson, Skiba-Szymanska, Ward, Shields, Felle, Farrer, Ritchie, and Penty]huwer2017quantum
  author author J. Huwer, author R. Stevenson,
  author J. Skiba-Szymanska,
  author M. Ward, author
  A. Shields, author M. Felle, author I. Farrer, author D. A.  Ritchie,  and author R. V.  Penty, @noop  journal journal Physical Review Applied volume 8,  pages 024007 (year 2017)NoStop
[Keiser(2003)]keiser2003optical
  author author G. Keiser, @noop  title Optical fiber
  communications (publisher Wiley Online Library, year 2003)NoStop
[Galtarossa et al.(2000)Galtarossa, Palmieri, Schiano, and  Tambosso]galtarossa2000statistical
  author author A. Galtarossa, author L. Palmieri, author M. Schiano,   and author T. Tambosso,  @noop  journal journal Optics Letters  volume 25, pages 1322 (year
  2000)NoStop
[Michler(2009)]michler2009single
  author author P. Michler, @noop  title Single semiconductor
  quantum dots, Vol. volume 231 (publisher
  Springer, year 2009)NoStop
[Stevenson et al.(2008)Stevenson, Hudson, Bennett, Young, Nicoll, Ritchie, and Shields]stevenson2008evolution
  author author R. M. Stevenson, author A. J. Hudson, author A. J. Bennett,
  author R. J. Young, author C. A. Nicoll, author
  D. A. Ritchie,  and author
  A. J. Shields, @noop  journal journal Physical Review Letters volume 101, pages 170501 (year
  2008)NoStop
[Ward et al.(2014)Ward,
  Dean, Stevenson, Bennett,
  Ellis, Cooper, Farrer,
  Nicoll, Ritchie, and Shields]ward2014coherent
  author author M. Ward, author M. Dean, author R. Stevenson, author
  A. Bennett, author D. Ellis, author K. Cooper, author I. Farrer, author C. Nicoll, author D. Ritchie,  and author A. Shields, @noop  journal journal Nature communications volume 5,  pages 3316 (year 2014)NoStop

