We coherently probe a quantum dot, strongly coupled to a photonic crystal nano-cavity, using a resonant laser beam. At higher pump power, the coupled systempsilas response becomes highly nonlinear. This coherent probing method has applications for classical and quantum information processing

Englund, Dirk

Faraon, Andrei

Fushman, Ilya

Vučković, Jelena

English

Caltech Authors - Main

Coherent Probing and Saturation of a Strongly Coupled Quantum Dot
Dirk Englund, Andrei Faraon, Ilya Fushman & Jelena Vucˇkovic´
Ginzton Laboratory, Stanford University, Stanford CA 94305
Abstract: We coherently probe a quantum dot, strongly coupled to a photonic crystal nano-cavity, using
a resonant laser beam. At higher pump power, the coupled system’s response becomes highly nonlinear.
This coherent probing method has applications for classical and quantum information processing.
c© 2007 Optical Society of America
OCIS codes: (270.1670 Coherent Optical Effects; (270.5580) Quantum Electrodynamics
Cavity quantum electrodynamics in solid state systems offers a scalable and robust platform for quantum
optics research and the development of quantum information processing applications. In this approach,
researchers aim to create a quantum network, which combines the utility of the photon as an information
carrier with the nonlinearity of an atomic system for interacting more than one quantum bit (qubit) in a gate.
The quantum network requires a way to coherently probe an atom or quantum dot in a cavity.
In this research, we present a novel method to probe a single InAs quantum dot (QD) that is strongly
coupled to a photonic crystal (PC) cavity, using a laser beam resonant with the quantum dot. We show
that the quantum dot strongly modifies the cavity transmission and reflection spectra [2]. Cavity-resonant
photons are prohibited from passing through the cavity at the QD resonance. At high probe intensity, the
quantum-dot induced reflectivity feature vanishes as the quantum dot becomes saturated. This giant optical
nonlinearity occurs at a level of one photon per quantum dot lifetime.
2 µm
Metal heating pad PC cavity
probe 
laser
Fig. 1. Photonic crystal structure.
The structure consists of a linear three-hole defect cavity in a triangular photonic crystal lattice, as shown in
Fig.1. It is fabricated in GaAs and contains a central layer of InAs quantum dots. The cavity has quality factor
Q = 104, as shown in the photoluminescence spectra in Fig.2(a). In this figure, the sample is maintained
near 25◦K while local temperature of the sample is scanned between spectra. The QD and cavity tune at
different rates, so that we can observe the anti-crossing behavior characteristic of a strongly coupled emitter
and cavity.
This system is then probed by reflecting a narrow-bandwidth laser beam that is near resonance with the
QD and cavity. By changing the probe wavelength, we probe the QD at different detunings with respect to
the cavity at low probe power. The reflectivity measurements are shown in Fig. 2(b). Instead a Lorentzian-
shaped cavity spectrum, a drop in the reflected signal is observed at the QD wavelength, as expected from
theory[1] (fits).
When the probe power is increased, we can explore the nonlinear behavior of the QD/cavity system. Fig.2(c)
shows the QD-induced reflectivity dip vanishing as Pin is increased. The saturation sets in as there is ap-
proximately one photon coupled to the cavity per modified quantum dot lifetime, which corresponds to an
average cavity photon population near one. We observe agreement with theory by a steady-state solution
       a806_1.pdf  
 
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0 20 40 60
25 nW
100 nW
300 nW
1 µW
3 µW
8 µW
scan count
0
R (experiment)
R (theory)
R (empty cavity)
=0.015
0.060
0.18
0.60
1.8
4.8
0
0
0
0
0
0
inc. power=
inc. power=
ncav
n      =cav
n      =cav
n      =cav
n      =cav
re
fle
cte
d 
int
en
sit
y (
no
rm
ali
ze
d)
n      =cav
50 100 150 200
0.2
0.4
0.6
0.8
1
scan count
In
te
ns
ity
 (n
or
m
ali
ze
d)
50 100 150 200 250
926.6
926.8
927.0
927.2
λ 
(n
m
)
R (theory)
R (Eq. 2)
R (experiment)
QD
Cavity
probe A
∆λ=0.021nm
(0.83g)
probe A
(a)
926.4 926.5 926.6 926.7 926.8 926.9
0
QD
Cavity
Cavity QD
(c)(b)
Fig. 2. (a) Photoluminescence measurements of a quantum dot strongly coupled to the photonic crystal nanocav-
ity. As local temperature is scanned, the QD and cavity tune at different rates and show anticrossing. (b) Reflec-
tivity of the probe beam off the same system. The bottom panel shows the tuning behavior of the quantum dot
and cavity. (c) The QD-induced reflectivity dip is saturated at an average intensity of ∼ 1 photon in the cavity.
of the quantum master equation (solid lines). We also verified that the QD-induced reflectivity dip vanishes
controllably when excitons are (incoherently) generated by excitation with an above-GaAs-bandgap laser
beam.
The measurements presented here provide both a novel method for probing the cavity-quantum dot system
and the first steps toward the realization of quantum devices based on coherent light scattering from quantum
dots in photonic crystal cavities. The giant optical nonlinearity is promising as a way to interact two or more
photons, enabling photon number detection and two-qubit gates. It may also find applications in classical
all-optical signal processing.
Financial support was provided by the ONR Young Investigator Award and MURI Center for photonic
quantum information systems (ARO/DTO Program). D.E. and I.F. were also supported by the NDSEG and
NSF fellowships. Work was performed in part at the Stanford Nanofabrication Facility of NNIN supported
by the National Science Foundation. We thank Nick Stoltz and Pierre Petroff of UC Santa Barbara for QD
material.
References
1. E. Waks and J. Vucˇkovic´. Dipole induced transparency in frop-filter cavity-waveguide systems. Physical Review Letters,
80(153601), April 2006.
2. D. Englund, A. Faraon, I. Fushman, N. Stoltz, P. Petroff, and J. Vuckovic Controlling Cavity Reflectivity with a Single
Quantum Dot. To be published in Nature (2007).
       a806_1.pdf  
 
© 2008 OSA / CLEO/QELS 2008
       QWF6.pdf  
 


Coherent probing and saturation of a strongly coupled quantum dot

Dipole induced transparency in frop-filter cavity-waveguide systems.

Vuckovic Controlling Cavity Reflectivity with a Single Quantum Dot.

https://authors.library.caltech.edu/34108/1/04573013.pdf

Coherent probing and saturation of a strongly coupled quantum dot

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