We demonstrate selective optical coupling of multiple, site controlled semiconductor quantum dots (QDs) to photonic crystal waveguide structures. The impact of the exact position and emission spectrum of the QDs on the coupling efficiency is elucidated. The influence of optical disorder and end-reflections on photon transport in these systems are discussed

de Lasson, Jakob Rosenkrantz

Dwir, Benjamin

Gregersen, Niels

Jarlov, Clément

Kapon, Elyahou

Kulkova, Irina

Lyasota, Alexey

Mørk, Jesper

Rigal, Bruno

Rudra, Alok

We demonstrate selective optical coupling of multiple, site controlled semiconductor quantum dots (QDs) to photonic crystal waveguide structures. The impact of the exact position and emission spectrum of the QDs on the coupling efficiency is elucidated. The influence of optical disorder and end-reflections on photon transport in these systems are discusse

Rigal, B.

Jarlov, C.

Dwir, B.

Rudra, A.

Lyasota, A.

Kulkova, I.

Kapon, E.

Online Research Database In Technology

Site-controlled quantum dots coupled to photonic crystal waveguides

We demonstrate selective optical coupling of multiple, site controlled semiconductor quantum dots (QDs) to photonic crystal waveguide structures. The impact of the exact position and emission spectrum of the QDs on the coupling efficiency is elucidated. The influence of optical disorder and end-reflections on photon transport in these systems are discussed.LP

Infoscience - École polytechnique fédérale de Lausanne

             1 Site-controlled quantum dots coupled to photonic crystal waveguides  B. Rigal1*, J. R. de Lasson2, C. Jarlov1, B. Dwir1, A. Rudra1, A. Lyasota1, I. Kulkova1, N. Gregersen2, J. Mørk2 and E. Kapon1 1Laboratory of physics of nanostructures (LPN), Ecole Polytechnique Fédérale de Lausanne, Switzerland  2DTU Fotonik, Department of Photonics Engineering, Technical University of Denmark, Denmark *corresponding author: bruno.rigal@epfl.ch  Abstract- We demonstrate selective optical coupling of multiple, site controlled semiconductor quantum dots (QDs) to photonic crystal waveguide structures. The impact of the exact position and emission spectrum of the QDs on the coupling efficiency is elucidated. The influence of optical disorder and end-reflections on photon transport in these systems are discussed.  The	challenging	goal	of	realizing	on-chip	quantum	circuits	in	which	spins	are	interfaced	with	photons	that	are	 then	routed,	processed	and	detected	has	 triggered	significant	 research	efforts	over	 the	past	decades	[1].	InGaAs/GaAs	quantum	dots	 (QDs)	 integrated	 in	photonic	crystal	 (PhC)	circuits	are	one	of	 the	most	advanced	technologies	 in	 this	 direction	[2].	Most	of	 the	work	has	 focused	on	 Stranski-Krastanow	QDs	 that	nucleate	 at	random	 positions	[3],	 while	 achieving	 truly	 scalable	 quantum	 circuits	 requires	 a	 precise	 deterministic	integration	of	an	entire	QD	system	in	a	photonic	circuit.	However,	the	inhomogeneous	broadening	inherent	to	QD	 systems	makes	 the	 simultaneous	 efficient	 coupling	 of	 several	QDs	 to	 a	 given	 photonic	mode	 difficult	 to	accomplish.	 On	 the	 contrary,	 the	 finite	 spectral	 bandwidth	 of	 photonic	 waveguides	 should	 facilitate	 the	simultaneous	optical	coupling	of	QD	systems.	Such	structures	could	be	used,	e.g.,	to	increase	the	emission	rate	of	single	photon	sources	by	efficiently	coupling	multiple	QD	single	photon	sources	to	the	same	optical	channel.	In	 this	 work,	 we	 demonstrate	 the	 deterministic	 coupling	 of	 five	 site-controlled	 QDs	 placed	 at	 different	positions	within	a	W1	semi-waveguide	with	a	reflective	termination	and	an	out-coupler	on	its	ends	(see	Fig.	1a).	We	study	the	spectra	emitted	by	the	s-states	of	each	single	QD	and	how	they	evolve	during	the	propagation	through	 the	 waveguide.	 In	 Fig.	 1b)	 spectrally	 resolved	 near-field	 pattern	 in	 which	 light	 is	 emitted	 by	 a	selectively	 excited	 QD	 positioned	 20.5µm	 away	 from	 the	 out-coupler,	 propagates	 in	 the	 waveguide	 and	 is	collected	at	the	out-coupler.	This	constitutes	the	first	direct	observation	of	 light	emission	by	a	site-controlled	QD	in	a	PhC	waveguide.	 	Next,	we	analyze	the	fraction	of	light	collected	at	the	out-coupler	relative	to	the	intensity	collected	directly	from	 the	QD	 emission	 (by	 exciting	 each	QD	 separately).	We	 perform	 the	 same	 study	 on	 each	QD	of	 eleven	structures	with	systematic	variations	in	the	PhC	hole	radii	r	such	that	the	QDs	s-states	(with	an	energy	around	1.31eV)	were	tuned	into	(r<72nm)	and	out	of	(r>72nm)	resonance	with	the	fundamental	waveguide	mode.	As	shown	in	Fig.	1c),	the	emission	of	QDs	in	the	bandgap	(r>72nm)	is	not	efficiently	channeled	to	the	out-coupler.	For	QDs	resonant	with	the	waveguide	photonic	band	(r<72nm),	the	fraction	of	light	collected	at	the	out-coupler	Ioutc/IQD	 reaches	values	up	to	10,	evidencing	an	efficient	coupling	of	 the	QDs	with	 the	waveguide	modes.	The	intensity	of	the	emission	collected	from	the	out-coupler	for	QDs	in	resonance	with	the	waveguide	band	varies	with	the	PhC	hole	radius.	This	is	explained	by	the	formation	of	Fabry	Pérot-like	modes	in	the	waveguide	due	to	 2 the	significant	reflection	at	 the	out-coupler	[4].	This	effect	 is	already	observed	 in	the	QD	spectra	collected	at	the	out-coupler	in	Fig.	1b:	only	QD	lines	near	resonance	with	a	Fabry	Pérot	line	are	efficiently	channeled	to	the	out-coupler.	A	minimal	reflection	at	the	out-coupler	 is	thus	required	 in	this	case	to	ensure	a	truly	broadband	coupling	of	the	QD	to	the	waveguide.	This	brings	to	light	the	need	for	alternative	designs	of	out-couplers	with	very	 low	 reflection	 into	 the	 waveguide.	 Photon	 correlation	 measurements	 confirm	 the	 emission	 of	 single	photons	 by	 the	 integrated	 QDs.	 The	 impact	 of	 PhC	 waveguide	 disorder	 on	 the	 propagation	 along	 the	 PhC	channel	 will	 also	 be	 demonstrated	 and	 discussed.	 We	 show	 that	 mode	 localization	 can	 be	 avoided	 when	propagation	via	modes	of	high	enough	frequency	is	used.	waveguide: 111a=25um20a=4.5um60 70 80r [nm]0510I outc/IQD(a)(b) (c)outcouplerQDsPosition [µm] 1020 0200110counts/s (log)Position [µm]101.3 1.32Energy [eV] 	Figure 1: (a) SEM picture of a 25µm long semi-waveguide with indications of QD positions, (b) Spectrally-resolved near field pattern of the structure in (a) (Excitation power: P=5µW, T=10K, r=61nm), only one QD (shown in green) is excited. (c) Effect of tuning the QD emission through the bandgap: fraction of the intensity extracted from the outcoupler divided by the intensity collected directly from the QD s-states as a function of the PhC hole radius (Excitation power: P=5µW, T=10K, for each PhC hole radius, each data point corresponds to the emission of only one of the five QDs). 	REFERENCES	1.	 	 	 R.-B.	Liu,	W.	Yao,	and	L.	J.	Sham,	"Quantum	computing	by	optical	control	of	electron	spins,"	Adv.	Phys.	59,	703–802	(2010).	2.	 	 	 C.	 P.	 Dietrich,	 A.	 Fiore,	M.	 Thompson,	M.	 Kamp,	 and	 S.	 Höfling,	 "GaAs	 integrated	 quantum	 photonics:	Towards	 dense	 and	 fully-functional	 quantum	 photonic	 integrated	 circuits,"	 ArXiv160106956	 Cond-Mat	Physicsquant-Ph	(2016).	3.	 	 	 P.	 Lodahl,	 S.	 Mahmoodian,	 and	 S.	 Stobbe,	 "Interfacing	 single	 photons	 and	 single	 quantum	 dots	 with	photonic	nanostructures,"	Rev.	Mod.	Phys.	87,	347	(2015).	4.	 	 	 M.	Arcari,	I.	Söllner,	A.	Javadi,	S.	L.	Hansen,	S.	Mahmoodian,	J.	Liu,	H.	Thyrrestrup,	E.	H.	Lee,	J.	D.	Song,	S.	Stobbe,	 and	 P.	 Lodahl,	 "Near-unity	 coupling	 efficiency	 of	 a	 quantum	 emitter	 to	 a	 photonic-crystal	waveguide,"	Phys.	Rev.	Lett.	113,	(2014).	

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Site-controlled quantum dots coupled to photonic crystal waveguides

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