Compact and electrically controllable on-chip sources of indistinguishable photons are desirable for the development of integrated quantum technologies. We demonstrate that two quantum dot light emitting diodes (LEDs) in close proximity on a single chip can function as a tunable, all-electric quantum light source. Light emitted by an electrically excited driving LED is used to excite quantum dots in the neighbouring diode. The wavelength of the quantum dot emission from the neighbouring driven diode is tuned via the quantum confined Stark effect. We also show that we can electrically tune the fine structure splitting.The authors acknowledge funding from the EPSRC for MBE system used for the growth of the QD-LED. E.M. and C.D. acknowledge support by the Marie Curie Actions within the Seventh Framework Programme for Research of the European Commission, under the Ini- tial Training Network PICQUE (Grant No. 608062) J. L. gratefully acknowledges financial support from the EPSRC CDT in Photonic Systems Development and Toshiba Research Europe Ltd

Bennett, AJ

Dangel, C

Ellis, DJP

Farrer, I

Lee, JP

Murray, E

Ritchie, DA

Shields, AJ

Spencer, P

arXiv

Compact and electrically controllable on-chip sources of indistinguishable photons are desirable for the development of integrated quantum technologies. We demonstrate that two quantum dot light emitting diodes (LEDs) in close proximity on a single chip can function as a tunable, all-electric quantum light source. Light emitted by an electrically excited driving LED is used to excite quantum dots in the neighbouring diode. The wavelength of the quantum dot emission from the neighbouring driven diode is tuned via the quantum confined Stark effect. We also show that we can electrically tune the fine structure splitting

Lee, J.P.

Murray, E.

Bennett, A.J.

Ellis, D.J.P.

Dangel, C.

Farrer, I.

Spencer, P.

Ritchie, D.A.

Shields, A.J.

White Rose Research Online

This is a repository copy of Electrically driven and electrically tunable quantum light sources.White Rose Research Online URL for this paper:http://eprints.whiterose.ac.uk/113225/Version: Accepted VersionArticle:Lee, J.P., Murray, E., Bennett, A.J. et al. (6 more authors) (2017) Electrically driven and electrically tunable quantum light sources. Applied Physics Letters, 110 (7). 071102. ISSN 0003-6951 https://doi.org/10.1063/1.4976197Published by AIP Publishing. Appl. Phys. Lett. 110, 071102 (2017); doi: http://dx.doi.org/10.1063/1.4976197.eprints@whiterose.ac.ukhttps://eprints.whiterose.ac.uk/Reuse Unless indicated otherwise, fulltext items are protected by copyright with all rights reserved. The copyright exception in section 29 of the Copyright, Designs and Patents Act 1988 allows the making of a single copy solely for the purpose of non-commercial research or private study within the limits of fair dealing. The publisher or other rights-holder may allow further reproduction and re-use of this version - refer to the White Rose Research Online record for this item. Where records identify the publisher as the copyright holder, users can verify any specific terms of use on the publisher’s website. Takedown If you consider content in White Rose Research Online to be in breach of UK law, please notify us by emailing eprints@whiterose.ac.uk including the URL of the record and the reason for the withdrawal request. Electrically driven and electrically tunable quantum light sourcesJ. P. Lee,1, 2 E. Murray,1, 3 A. J. Bennett,1, ∗ D. J. P. Ellis,1 C.Dangel,1, 3, 4 I. Farrer,3, † P. Spencer,3 D. A. Ritchie,3 and A. J. Shields11Toshiba Research Europe Limited, Cambridge Research Laboratory,208 Science Park, Milton Road, Cambridge, CB4 0GZ, U.K.2Engineering Department, Cambridge University,9 J. J. Thomson Avenue, Cambridge, CB3 0FA, U.K.3Cavendish Laboratory, Cambridge University,J. J. Thomson Avenue, Cambridge, CB3 0HE, U.K.4Physik Department, Technische Universität München,85748 Garching, Germany(Dated: December 15, 2016)Compact and electrically controllable on-chip sources of indistinguishable photons are desirablefor the development of integrated quantum technologies. We demonstrate that two quantum dotlight emitting diodes (LEDs) in close proximity on a single chip can function as a tunable, all-electricquantum light source. Light emitted by an electrically excited driving LED is used to excite quantumdots the neighbouring diode. The wavelength of the quantum dot emission from the neighbouringdriven diode is tuned via the quantum confined Stark effect. We also show that we can electricallytune the fine structure splitting.Sources of indistinguishable single photons or entan-gled photon pairs have applications in quantum key dis-tribution [1, 2], quantum teleportation [3], imaging [4]and linear optical quantum computing [5].Self assembled quantum dots (QDs) can be used insolid-state quantum light sources. In an InAs QD thedecay of a bright neutral or singly charged exciton re-sults in the emission of a single photon [6]. Furthermore,the biexciton cascade of a QD has been used to gener-ate on-demand entangled photon pairs [7]. These QDsare produced using well-developed semiconductor fabri-cation techniques, allowing them to be integrated intosemiconductor devices and photonic cavities.An ongoing challenge of working with self assembledquantum dots is their random distribution in the size,shape and chemical composition, which leads to a ran-dom distribution in the wavelength of the emitted pho-tons. The distribution in transition energies is over 104times the width of each individual line, consequently theprobability of two randomly chosen quantum dots hav-ing emission lines at the same wavelength is less than10−4 [8]. Any difference in wavelength between photonsmakes them distinguishable. Clearly this obstacle mustbe overcome in order to realise the many applications ofquantum light sources that make use of Hong-Ou-Mandel(HOM) interference, which requires the photons to be in-distinguishable.Several methods of tuning the emission wavelengths ofquantum dots in-situ have been explored, including vary-ing the temperature [9], magnetic field [10], strain [11]and electric field [12]. The latter approach is very promis-∗ anthony.bennett@crl.toshiba.co.uk† Current affiliation: Department of Electronic & Electrical En-gineering, University of Sheffield, Mappin Street, Sheffield, S13JD, U.K.ing as it allows for individual tuning of many closelyspaced devices suitable for producing compact integratedquantum technologies. We note that although strain tun-ing is usually applied to a whole device, recently a devicewas developed that would in principle be suitable for theproduction of multiple strain tuned diodes [13]. Straintuning can also be used in tandem with electric tuning inorder to allow independent control over the exciton andbiexciton energies [14].FIG. 1. An illustration of the devices used. The deviceshave a p-doped region (red), an intrinsic region (clear) andan n-doped region (blue). A LED driven strongly in forwardbias (left) emits light (shown as a blue beam), which excitesquantum dots in a neighbouring device (right). The quantumdots emit anti-bunched light (green).Applying a vertical electric field to a QD causes thetransitions to undergo a Stark shift, which tunes thewavelength of the emitted photons. In most devices, ap-plying an electric field of over −60 kV cm−1 can result inthe quenching of emission [15]. This can be increased byan order of magnitude by embedding the quantum dots in2850900950Diode 2Diode 1Wetting layeremissionEmission (a.u.)Wavelength (nm)Non-radiativedecayQuantum dotemissionWetting layerabsorptionEmission / Absorption (a.u.)FIG. 2. A diagram showing the principle of operation - Lightemitted from the wetting layer of Diode 1 is absorbed by thewetting layer of Diode 2, generating charge carriers in Diode2. The charge carriers can be captured by quantum dotsin Diode 2 resulting in quantum light emission. The wettinglayer emission (left) and the quantum dot emission (right) arereal data, the wetting layer absorption shown is a duplicate ofthe emission data and is included solely to show the principleof operation of the device.2.0 2.5 3.0 3.5Quantum light emission from Diode 2 (a.u.)Voltage across Diode 1 (V)0 1 20.00.51.01.52.02.5Current through Diode 1 (mA)Voltage across Diode 1 (V)FIG. 3. A graph showing the current through Diode 1 as afunction of voltage. The device shows diode like behaviour.Inset: Quantum light emission from Diode 2 as a functionof the voltage across Diode 1. Note that the emission andcurrent both ‘turn on’ at ∼ 2.25 V.a GaAs/AlGaAs quantum well, resulting in an increasedtuning range [16]. These structures have been used todemonstrate electric control of a spin [17], tuning of theg-factor of trapped spins [18] and tuning of the fine struc-ture splitting (FSS) [19, 20]. A small FSS is required toproduce entangled photons from the bi-exciton cascade.The key advantages of electrically tunable devices arethat many individually tunable devices can be producedon a single chip using standard photo-lithographic semi-conductor processing techniques and, unlike piezo-tunedsystems, they do not suffer from long term drift [21].For the development of compact and scalable quan-tum technologies, the capability to electrically trigger the-350 -300 -250 -200 -150 -100 -5092593093501X +XNormalisedIntensity  Electric Field (kV cm-1)Wavelength (nm)0.00010002000300040005000X -FIG. 4. The emission spectrum of Diode 2 (driven by Diode1) as a function of applied electric field. Tuning of over 5 nmis visible.FIG. 5. The second-order correlation function of a singleemission line from Diode 2. Inset:) The fine structure split-ting of a neutral exciton as a function of the electric fieldacross Diode 2.generation of photons is desirable and has lead to the de-velopment of a single photon [22] and entangled photon[23] light emitting diodes. Combining the advantages ofwavelength tuning and electrical excitation of quantumdots would allow the electrically triggered generation ofindistinguishable photons from different sources.In this paper we demonstrate a method of producingelectrically triggered anti-bunched light from an electri-cally tunable source. The device is fabricated from a sec-tion of a single wafer and contains 16 individually tunablediode structures on a single chip.The devices used in this study are 180µm×210µm pla-nar microcavity LEDs containing a layer of InAs quan-tum dots embedded in a 10 nm GaAs quantum well withAl0.75Ga0.25As barriers. Distributed Bragg Reflectors(DBRs) grown above (4 repeats) and below the InAs(15 repeats) quantum dot layer and quantum well areused to form a half-wavelength cavity. This unbalancedcavity both increases the portion of QD light emittedvertically and acts as a horizontal waveguide for opticalemission from the InAs wetting layer. The top DBR isdoped p-type and the bottom DBR is doped n-type to3form a diode structure suitable for electrical excitation.The key idea is to use light produced by one LED toexcite the QDs in the neighbouring diode. We run oneLED (Diode 1) in forward bias, resulting in broadbandemission from the InAs wetting layer. The emitted lightis guided horizontally due to the Bragg reflectors aboveand below the wetting layer. A portion of the emittedlight is incident on the neighbouring LED (Diode 2) andwill be absorbed by the wetting layer, generating exci-tons. These will be subsequently captured by quantumdots in Diode 2 resulting in quantum light emission (seefigures 1 and 2). This on-chip in plane excitation schemeis similar to the scheme presented in [24], which makesuse of a whispering-gallery-mode QD laser to excite a QDembedded in a nearby micropillar.The cavity mode of the planar microcavity matches theemission wavelength of the quantum dots of interest, in-creasing the proportion of QD emission directed upwardsinto the collection optics. Varying the bias across Diode2 allows wavelength tuning by Stark shifting the tran-sitions. The quantum dots are embedded in a quantumwell (as in [16]) in order to increase the maximum voltagethat can be applied without quenching the emission.The intensity of light emission from Diode 2 can becontrolled by varying the voltage across Diode 1 and thedevices show good diode-like behaviour (figure 3). Weapply a voltage of 2.5V (corresponding to a current den-sity of ∼ 23 A cm−2) to Diode 1, resulting in a broademission spectrum with a peak at around 870 nm corre-sponding to the InAs wetting layer (figure 2). Figure 4shows the observed emission spectrum of a QD in Diode2 as a function of the applied electric field - a Stark shiftof over 5 nm is visible.A diffraction grating was used to spectrally filter theoutput of Diode 2 to pick out light from a single emissionline. The filtered light was then directed into a HanburyBrown and Twiss setup in order to perform a second-order correlation function (g(2)(τ)) measurement. Theresult can be seen in figure 5). We observe a dip ing(2)(τ) as τ approaches 0, giving g(2)(0) = 0.06, belowthe g(2)(0) < 0.5 threshold, which shows the output isdominated by light from a single quantum emitter. Thisis an order of improvement on the values of g(2)(0) mea-sured in prior demonstrations of on-chip in-plane excita-tion [25]. We note that g(2)(0) 6= 0, even though we haveaccounted for the detector response. We attribute thisto the leakage of light from Diode 1 into the output.Finally, we demonstrate that we can tune the FSS asa function of electric field. The inset in figure 5 showsfine structure splitting of an exciton in Diode 2 as a func-tion of the electric field across Diode 2, indicating thatthese devices could be used as sources of entangled pho-ton pairs.In the future we can envisage a number of changes thatwould increase the efficiency of the device. For example,Diode 1 could be structured to increase the directionalityof emission towards Diode 2 by means of a unidirectionalantenna. Similarly, a waveguide between the LEDs couldincrease the cross-coupling efficiency, with in principleone driving LED exciting many tunable LEDs. The use offast electronics and low RC constant devices could allow‘on-demand’ emission by either varying the bias to diode1 to modulate the ‘pump’ (a possibility which is alsohinted at in [25]) or by varying the bias to Diode 2 tomodulate the wavelength.We have demonstrated an all-electric tunable quantumsource fabricated using a simple photo-lithographic pro-cess. While this is a proof-of-principle device intendedto demonstrate the possibility of an electrically tunableand electrically driven quantum light source, we antici-pate that future work will improve the coupling betweendriven and driving LEDs and lead to the production ofdevices suitable for compact multiplexed on-chip quan-tum optics technologies.AcknowledgmentsThe authors acknowledge funding from the EPSRCfor MBE system used for the growth of the QD-LED.E.M. and C.D. acknowledge support by the Marie CurieActions within the Seventh Framework Programme forResearch of the European Commission, under the Ini-tial Training Network PICQUE (Grant No. 608062) J.L. gratefully acknowledges financial support from theEPSRC CDT in Photonic Systems Development andToshiba Research Europe Ltd.Data AccessThe experimental data used to produce the figures inthis paper is publicly available at ‘DOI here’. [Permanentlink to be included before publication][1] C. H. Bennett, in International Conference on ComputerSystem and Signal Processing, IEEE, 1984 (1984) pp.175–179.[2] A. K. Ekert, Phys. Rev. Lett. 67, 661 (1991).[3] C. H. Bennett, G. Brassard, C. Crépeau, R. Jozsa,A. Peres, and W. K. Wootters, Phys. Rev. Lett. 70,1895 (1993).[4] L. A. Lugiato, A. Gatti, and E. Brambilla, Journal of Op-tics B: Quantum and Semiclassical Optics 4, S176 (2002).[5] E. Knill, R. Laflamme, and G. J. Milburn, Nature 409,46 (2001).[6] S. Buckley, K. Rivoire, and J. Vuckovic, Reports onProgress in Physics 75, 126503 (2012).[7] R. M. Stevenson, R. J. Young, P. Atkinson, K. Cooper,D. A. Ritchie, and A. J. Shields, Nature 439, 179 (2006).4[8] R. Trotta, J. Mart́ın-Sánchez, I. Daruka, C. Ortix, andA. Rastelli, Phys. Rev. Lett. 114, 150502 (2015).[9] D. G. Gevaux, A. J. Bennett, R. M. Stevenson, A. J.Shields, P. Atkinson, J. Griffiths, D. Anderson, G. A. C.Jones, and D. A. Ritchie, Applied Physics Letters 88,131101 (2006), http://dx.doi.org/10.1063/1.2189747.[10] S. Reitzenstein, S. Münch, P. Franeck, A. Rahimi-Iman,A. Löffler, S. Höfling, L. Worschech, and A. Forchel,Phys. Rev. Lett. 103, 127401 (2009).[11] S. Seidl, A. Högele, M. Kroner, K. Karrai, A. Badolato,P. Petroff, and R. Warburton, Physica E: Low-dimensional Systems and Nanostructures 32, 14 (2006),proceedings of the 12th International Conference onModulated Semiconductor StructuresProceedings of the12th International Conference on Modulated Semicon-ductor Structures.[12] F. Findeis, M. Baier, E. Beham, A. Zrenner, and G. Ab-streiter, Applied Physics Letters 78, 2958 (2001).[13] R. Trotta, P. Atkinson, J. Plumhof, E. Zallo, R. O.Rezaev, S. Kumar, S. Baunack, J. Schröter, A. Rastelli,and O. Schmidt, Advanced materials 24, 2668 (2012).[14] R. Trotta, E. Zallo, E. Magerl, O. G. Schmidt, andA. Rastelli, Physical Review B 88, 155312 (2013).[15] R. Oulton, J. J. Finley, A. D. Ashmore, I. S. Gregory,D. J. Mowbray, M. S. Skolnick, M. J. Steer, S.-L. Liew,M. A. Migliorato, and A. J. Cullis, Phys. Rev. B 66,045313 (2002).[16] R. B. Patel, A. J. Bennett, I. Farrer, C. A. Nicoll, D. A.Ritchie, and A. J. Shields, Nature photonics 4, 632(2010).[17] A. B. De La Giroday, A. Bennett, M. Pooley, R. Steven-son, N. Sköld, R. Patel, I. Farrer, D. Ritchie, andA. Shields, Physical Review B 82, 241301 (2010).[18] A. J. Bennett, M. A. Pooley, Y. Cao, N. Sköld, I. Farrer,D. A. Ritchie, and A. J. Shields, Nature communications4, 1522 (2013).[19] A. Bennett, M. Pooley, R. Stevenson, M. Ward, R. Pa-tel, A. B. de La Giroday, N. Sköld, I. Farrer, C. Nicoll,D. Ritchie, et al., Nature Physics 6, 947 (2010).[20] M. Ward, M. Dean, R. Stevenson, A. Bennett, D. El-lis, K. Cooper, I. Farrer, C. Nicoll, D. Ritchie, andA. Shields, Nature communications 5 (2014).[21] J. Zhang, J. S. Wildmann, F. Ding, R. Trotta, Y. Huo,E. Zallo, D. Huber, A. Rastelli, and O. G. Schmidt,Nature communications 6 (2015).[22] Z. Yuan, B. E. Kardynal, R. M. Stevenson, A. J.Shields, C. J. Lobo, K. Cooper, N. S. Beattie, D. A.Ritchie, and M. Pepper, Science 295, 102 (2002),http://science.sciencemag.org/content/295/5552/102.full.pdf.[23] C. Salter, R. Stevenson, I. Farrer, C. Nicoll, D. Ritchie,and A. Shields, Nature 465, 594 (2010).[24] E. Stock, F. Albert, C. Hopfmann, M. Lermer, C. Schnei-der, S. Höfling, A. Forchel, M. Kamp, and S. Reitzen-stein, Advanced Materials 25, 707 (2013).[25] P. Munnelly, T. Heindel, M. M. Karow, S. Höfling,M. Kamp, C. Schneider, and S. Reitzenstein, IEEE Jour-nal of Selected Topics in Quantum Electronics 21, 681(2015).

Electrically driven and electrically tunable quantum light sources

J. P. Lee

E. Murray

A. J. Bennett

D. J. P. Ellis

C. Dangel

I. Farrer

P. Spencer

D. A. Ritchie

A. J. Shields

Crossref

Applied Physics Letters

Electrically driven and electrically tunable quantum light           sources

Apollo (Cambridge)

Electrically driven and electrically tunable quantum light sourcesJ. P. Lee,1, 2 E. Murray,1, 3 A. J. Bennett,1, ∗ D. J. P. Ellis,1 C.Dangel,1, 3, 4 I. Farrer,3, † P. Spencer,3 D. A. Ritchie,3 and A. J. Shields11Toshiba Research Europe Limited, Cambridge Research Laboratory,208 Science Park, Milton Road, Cambridge, CB4 0GZ, U.K.2Engineering Department, Cambridge University,9 J. J. Thomson Avenue, Cambridge, CB3 0FA, U.K.3Cavendish Laboratory, Cambridge University,J. J. Thomson Avenue, Cambridge, CB3 0HE, U.K.4Physik Department, Technische Universita¨t Mu¨nchen,85748 Garching, Germany(Dated: December 15, 2016)Compact and electrically controllable on-chip sources of indistinguishable photons are desirablefor the development of integrated quantum technologies. We demonstrate that two quantum dotlight emitting diodes (LEDs) in close proximity on a single chip can function as a tunable, all-electricquantum light source. Light emitted by an electrically excited driving LED is used to excite quantumdots the neighbouring diode. The wavelength of the quantum dot emission from the neighbouringdriven diode is tuned via the quantum confined Stark effect. We also show that we can electricallytune the fine structure splitting.Sources of indistinguishable single photons or entan-gled photon pairs have applications in quantum key dis-tribution [1, 2], quantum teleportation [3], imaging [4]and linear optical quantum computing [5].Self assembled quantum dots (QDs) can be used insolid-state quantum light sources. In an InAs QD thedecay of a bright neutral or singly charged exciton re-sults in the emission of a single photon [6]. Furthermore,the biexciton cascade of a QD has been used to gener-ate on-demand entangled photon pairs [7]. These QDsare produced using well-developed semiconductor fabri-cation techniques, allowing them to be integrated intosemiconductor devices and photonic cavities.An ongoing challenge of working with self assembledquantum dots is their random distribution in the size,shape and chemical composition, which leads to a ran-dom distribution in the wavelength of the emitted pho-tons. The distribution in transition energies is over 104times the width of each individual line, consequently theprobability of two randomly chosen quantum dots hav-ing emission lines at the same wavelength is less than10−4 [8]. Any difference in wavelength between photonsmakes them distinguishable. Clearly this obstacle mustbe overcome in order to realise the many applications ofquantum light sources that make use of Hong-Ou-Mandel(HOM) interference, which requires the photons to be in-distinguishable.Several methods of tuning the emission wavelengths ofquantum dots in-situ have been explored, including vary-ing the temperature [9], magnetic field [10], strain [11]and electric field [12]. The latter approach is very promis-∗ anthony.bennett@crl.toshiba.co.uk† Current affiliation: Department of Electronic & Electrical En-gineering, University of Sheffield, Mappin Street, Sheffield, S13JD, U.K.ing as it allows for individual tuning of many closelyspaced devices suitable for producing compact integratedquantum technologies. We note that although strain tun-ing is usually applied to a whole device, recently a devicewas developed that would in principle be suitable for theproduction of multiple strain tuned diodes [13]. Straintuning can also be used in tandem with electric tuning inorder to allow independent control over the exciton andbiexciton energies [14].FIG. 1. An illustration of the devices used. The deviceshave a p-doped region (red), an intrinsic region (clear) andan n-doped region (blue). A LED driven strongly in forwardbias (left) emits light (shown as a blue beam), which excitesquantum dots in a neighbouring device (right). The quantumdots emit anti-bunched light (green).Applying a vertical electric field to a QD causes thetransitions to undergo a Stark shift, which tunes thewavelength of the emitted photons. In most devices, ap-plying an electric field of over −60 kV cm−1 can result inthe quenching of emission [15]. This can be increased byan order of magnitude by embedding the quantum dots in2850900950Diode 2Diode 1Wetting layeremissionEmission (a.u.)Wavelength (nm)Non-radiativedecayQuantum dotemissionWetting layerabsorptionEmission / Absorption (a.u.)FIG. 2. A diagram showing the principle of operation - Lightemitted from the wetting layer of Diode 1 is absorbed by thewetting layer of Diode 2, generating charge carriers in Diode2. The charge carriers can be captured by quantum dotsin Diode 2 resulting in quantum light emission. The wettinglayer emission (left) and the quantum dot emission (right) arereal data, the wetting layer absorption shown is a duplicate ofthe emission data and is included solely to show the principleof operation of the device.2.0 2.5 3.0 3.5Quantum light emission from Diode 2 (a.u.)Voltage across Diode 1 (V)0 1 20.00.51.01.52.02.5Current through Diode 1 (mA)Voltage across Diode 1 (V)FIG. 3. A graph showing the current through Diode 1 as afunction of voltage. The device shows diode like behaviour.Inset: Quantum light emission from Diode 2 as a functionof the voltage across Diode 1. Note that the emission andcurrent both ‘turn on’ at ∼ 2.25 V.a GaAs/AlGaAs quantum well, resulting in an increasedtuning range [16]. These structures have been used todemonstrate electric control of a spin [17], tuning of theg-factor of trapped spins [18] and tuning of the fine struc-ture splitting (FSS) [19, 20]. A small FSS is required toproduce entangled photons from the bi-exciton cascade.The key advantages of electrically tunable devices arethat many individually tunable devices can be producedon a single chip using standard photo-lithographic semi-conductor processing techniques and, unlike piezo-tunedsystems, they do not suffer from long term drift [21].For the development of compact and scalable quan-tum technologies, the capability to electrically trigger the-350 -300 -250 -200 -150 -100 -5092593093501X +XNormalisedIntensity  Electric Field (kV cm-1)Wavelength (nm)0.00010002000300040005000X -FIG. 4. The emission spectrum of Diode 2 (driven by Diode1) as a function of applied electric field. Tuning of over 5 nmis visible.FIG. 5. The second-order correlation function of a singleemission line from Diode 2. Inset:) The fine structure split-ting of a neutral exciton as a function of the electric fieldacross Diode 2.generation of photons is desirable and has lead to the de-velopment of a single photon [22] and entangled photon[23] light emitting diodes. Combining the advantages ofwavelength tuning and electrical excitation of quantumdots would allow the electrically triggered generation ofindistinguishable photons from different sources.In this paper we demonstrate a method of producingelectrically triggered anti-bunched light from an electri-cally tunable source. The device is fabricated from a sec-tion of a single wafer and contains 16 individually tunablediode structures on a single chip.The devices used in this study are 180µm×210µm pla-nar microcavity LEDs containing a layer of InAs quan-tum dots embedded in a 10 nm GaAs quantum well withAl0.75Ga0.25As barriers. Distributed Bragg Reflectors(DBRs) grown above (4 repeats) and below the InAs(15 repeats) quantum dot layer and quantum well areused to form a half-wavelength cavity. This unbalancedcavity both increases the portion of QD light emittedvertically and acts as a horizontal waveguide for opticalemission from the InAs wetting layer. The top DBR isdoped p-type and the bottom DBR is doped n-type to3form a diode structure suitable for electrical excitation.The key idea is to use light produced by one LED toexcite the QDs in the neighbouring diode. We run oneLED (Diode 1) in forward bias, resulting in broadbandemission from the InAs wetting layer. The emitted lightis guided horizontally due to the Bragg reflectors aboveand below the wetting layer. A portion of the emittedlight is incident on the neighbouring LED (Diode 2) andwill be absorbed by the wetting layer, generating exci-tons. These will be subsequently captured by quantumdots in Diode 2 resulting in quantum light emission (seefigures 1 and 2). This on-chip in plane excitation schemeis similar to the scheme presented in [24], which makesuse of a whispering-gallery-mode QD laser to excite a QDembedded in a nearby micropillar.The cavity mode of the planar microcavity matches theemission wavelength of the quantum dots of interest, in-creasing the proportion of QD emission directed upwardsinto the collection optics. Varying the bias across Diode2 allows wavelength tuning by Stark shifting the tran-sitions. The quantum dots are embedded in a quantumwell (as in [16]) in order to increase the maximum voltagethat can be applied without quenching the emission.The intensity of light emission from Diode 2 can becontrolled by varying the voltage across Diode 1 and thedevices show good diode-like behaviour (figure 3). Weapply a voltage of 2.5V (corresponding to a current den-sity of ∼ 23 A cm−2) to Diode 1, resulting in a broademission spectrum with a peak at around 870 nm corre-sponding to the InAs wetting layer (figure 2). Figure 4shows the observed emission spectrum of a QD in Diode2 as a function of the applied electric field - a Stark shiftof over 5 nm is visible.A diffraction grating was used to spectrally filter theoutput of Diode 2 to pick out light from a single emissionline. The filtered light was then directed into a HanburyBrown and Twiss setup in order to perform a second-order correlation function (g(2)(τ)) measurement. Theresult can be seen in figure 5). We observe a dip ing(2)(τ) as τ approaches 0, giving g(2)(0) = 0.06, belowthe g(2)(0) < 0.5 threshold, which shows the output isdominated by light from a single quantum emitter. Thisis an order of improvement on the values of g(2)(0) mea-sured in prior demonstrations of on-chip in-plane excita-tion [25]. We note that g(2)(0) 6= 0, even though we haveaccounted for the detector response. We attribute thisto the leakage of light from Diode 1 into the output.Finally, we demonstrate that we can tune the FSS asa function of electric field. The inset in figure 5 showsfine structure splitting of an exciton in Diode 2 as a func-tion of the electric field across Diode 2, indicating thatthese devices could be used as sources of entangled pho-ton pairs.In the future we can envisage a number of changes thatwould increase the efficiency of the device. For example,Diode 1 could be structured to increase the directionalityof emission towards Diode 2 by means of a unidirectionalantenna. Similarly, a waveguide between the LEDs couldincrease the cross-coupling efficiency, with in principleone driving LED exciting many tunable LEDs. The use offast electronics and low RC constant devices could allow‘on-demand’ emission by either varying the bias to diode1 to modulate the ‘pump’ (a possibility which is alsohinted at in [25]) or by varying the bias to Diode 2 tomodulate the wavelength.We have demonstrated an all-electric tunable quantumsource fabricated using a simple photo-lithographic pro-cess. While this is a proof-of-principle device intendedto demonstrate the possibility of an electrically tunableand electrically driven quantum light source, we antici-pate that future work will improve the coupling betweendriven and driving LEDs and lead to the production ofdevices suitable for compact multiplexed on-chip quan-tum optics technologies.AcknowledgmentsThe authors acknowledge funding from the EPSRCfor MBE system used for the growth of the QD-LED.E.M. and C.D. acknowledge support by the Marie CurieActions within the Seventh Framework Programme forResearch of the European Commission, under the Ini-tial Training Network PICQUE (Grant No. 608062) J.L. gratefully acknowledges financial support from theEPSRC CDT in Photonic Systems Development andToshiba Research Europe Ltd.Data AccessThe experimental data used to produce the figures inthis paper is publicly available at ‘DOI here’. [Permanentlink to be included before publication][1] C. H. Bennett, in International Conference on ComputerSystem and Signal Processing, IEEE, 1984 (1984) pp.175–179.[2] A. K. Ekert, Phys. Rev. Lett. 67, 661 (1991).[3] C. H. Bennett, G. Brassard, C. Cre´peau, R. Jozsa,A. Peres, and W. K. Wootters, Phys. Rev. Lett. 70,1895 (1993).[4] L. A. Lugiato, A. Gatti, and E. Brambilla, Journal of Op-tics B: Quantum and Semiclassical Optics 4, S176 (2002).[5] E. Knill, R. Laflamme, and G. J. Milburn, Nature 409,46 (2001).[6] S. Buckley, K. Rivoire, and J. Vuckovic, Reports onProgress in Physics 75, 126503 (2012).[7] R. M. Stevenson, R. J. Young, P. Atkinson, K. Cooper,D. A. Ritchie, and A. J. Shields, Nature 439, 179 (2006).4[8] R. Trotta, J. Mart´ın-Sa´nchez, I. Daruka, C. Ortix, andA. Rastelli, Phys. Rev. Lett. 114, 150502 (2015).[9] D. G. Gevaux, A. J. Bennett, R. M. Stevenson, A. J.Shields, P. Atkinson, J. Griffiths, D. Anderson, G. A. C.Jones, and D. A. Ritchie, Applied Physics Letters 88,131101 (2006), http://dx.doi.org/10.1063/1.2189747.[10] S. Reitzenstein, S. Mu¨nch, P. Franeck, A. Rahimi-Iman,A. Lo¨ﬄer, S. Ho¨fling, L. Worschech, and A. Forchel,Phys. Rev. Lett. 103, 127401 (2009).[11] S. Seidl, A. Ho¨gele, M. Kroner, K. Karrai, A. Badolato,P. Petroff, and R. Warburton, Physica E: Low-dimensional Systems and Nanostructures 32, 14 (2006),proceedings of the 12th International Conference onModulated Semiconductor StructuresProceedings of the12th International Conference on Modulated Semicon-ductor Structures.[12] F. Findeis, M. Baier, E. Beham, A. Zrenner, and G. Ab-streiter, Applied Physics Letters 78, 2958 (2001).[13] R. Trotta, P. Atkinson, J. Plumhof, E. Zallo, R. O.Rezaev, S. Kumar, S. Baunack, J. Schro¨ter, A. Rastelli,and O. Schmidt, Advanced materials 24, 2668 (2012).[14] R. Trotta, E. Zallo, E. Magerl, O. G. Schmidt, andA. Rastelli, Physical Review B 88, 155312 (2013).[15] R. Oulton, J. J. Finley, A. D. Ashmore, I. S. Gregory,D. J. Mowbray, M. S. Skolnick, M. J. Steer, S.-L. Liew,M. A. Migliorato, and A. J. Cullis, Phys. Rev. B 66,045313 (2002).[16] R. B. Patel, A. J. Bennett, I. Farrer, C. A. Nicoll, D. A.Ritchie, and A. J. Shields, Nature photonics 4, 632(2010).[17] A. B. De La Giroday, A. Bennett, M. Pooley, R. Steven-son, N. Sko¨ld, R. Patel, I. Farrer, D. Ritchie, andA. Shields, Physical Review B 82, 241301 (2010).[18] A. J. Bennett, M. A. Pooley, Y. Cao, N. Sko¨ld, I. Farrer,D. A. Ritchie, and A. J. Shields, Nature communications4, 1522 (2013).[19] A. Bennett, M. Pooley, R. Stevenson, M. Ward, R. Pa-tel, A. B. de La Giroday, N. Sko¨ld, I. Farrer, C. Nicoll,D. Ritchie, et al., Nature Physics 6, 947 (2010).[20] M. Ward, M. Dean, R. Stevenson, A. Bennett, D. El-lis, K. Cooper, I. Farrer, C. Nicoll, D. Ritchie, andA. Shields, Nature communications 5 (2014).[21] J. Zhang, J. S. Wildmann, F. Ding, R. Trotta, Y. Huo,E. Zallo, D. Huber, A. Rastelli, and O. G. Schmidt,Nature communications 6 (2015).[22] Z. Yuan, B. E. Kardynal, R. M. Stevenson, A. J.Shields, C. J. Lobo, K. Cooper, N. S. Beattie, D. A.Ritchie, and M. Pepper, Science 295, 102 (2002),http://science.sciencemag.org/content/295/5552/102.full.pdf.[23] C. Salter, R. Stevenson, I. Farrer, C. Nicoll, D. Ritchie,and A. Shields, Nature 465, 594 (2010).[24] E. Stock, F. Albert, C. Hopfmann, M. Lermer, C. Schnei-der, S. Ho¨fling, A. Forchel, M. Kamp, and S. Reitzen-stein, Advanced Materials 25, 707 (2013).[25] P. Munnelly, T. Heindel, M. M. Karow, S. Ho¨fling,M. Kamp, C. Schneider, and S. Reitzenstein, IEEE Jour-nal of Selected Topics in Quantum Electronics 21, 681(2015).

Electrically driven and electrically tunable quantum light sources

Abstract

Similar works

Full text

Available Versions

White Rose Research Online

Crossref

Apollo (Cambridge)

Online Research @ Cardiff