17 research outputs found
Sub-Natural Linewidth Single Photons from a Quantum Dot
The observation of quantum dot resonance fluorescence enabled a new
solid-state approach to generating single photons with a bandwidth almost as
narrow as the natural linewidth of a quantum dot transition. Here, we operate
in the Heitler regime of resonance fluorescence to generate sub-natural
linewidth and high-coherence quantum light from a single quantum dot. The
measured single-photon bandwidth exhibits a 30-fold reduction with respect to
the radiative linewidth of the QD transition and the single photons exhibit
coherence properties inherited from the excitation laser. In contrast,
intensity-correlation measurements reveal that this photon source maintains a
high degree of antibunching behaviour on the order of the transition lifetime
with vanishing two-photon scattering probability. This light source will find
immediate applications in quantum cryptography, measurement-based quantum
computing and, in particular, deterministic generation of high-fidelity
distributed entanglement among independent and even disparate quantum systems
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Coherent photons from a solid-state artificial atom
Single spins confined in semiconductor quantum dots - artificial atoms in the solid-state - are attractive candidates for quantum mechanical bits, the fundamental units and building blocks of a quantum computer. The ability to address quantum dot spins optically allows us to initialise and manipulate the state of the quantum bit. Gaining information on the qubit, for example by reading out its state, not only requires state-selective optical excitation, but also access to the single photons scattered in response by the quantum dot. Further, for a distributed computer architecture where nodes of few quantum bits are interlinked via optical communication channels photonic quantum bits are required to faithfully transmit the quantum information.
In this thesis we advocate resonant excitation of quantum dot transitions and collection of the resonance fluorescence to address two outstanding challenges: generating dephasing-free single photons for use as flying quantum bits and single-shot spin readout. To this end we investigate the spectral and first-order coherence properties of quantum dot resonance fluorescence. In particular, we directly observe highly coherent scattering in the low Rabi frequency limit which has remained unexplored for solid-state single photon emitters so far.
At the same time, interactions with the semiconductor environment are revealed and quantified through their optical signatures: exciton-phonon coupling, nuclear spin dynamics and local electric field fluctuations signal a departure from the ideal atom-like behaviour.
Taking advantage of the laser-like coherence of single phase-locked quantum dot photons in the Heitler regime, we demonstrate near-ideal two-photon quantum interference. This benchmark measurement is a precursor for the photonic entanglement of distant quantum dot spins in a quantum optical network, and the results here predict a high fidelity operation.
Finally, moving to tunnel-coupled quantum dot molecules we show that the overlap of carrier wave functions in two closely spaced quantum dots forms new spin-selective optical transitions not available in single quantum dots. Then, the presence or absence of scattered photons reveals the electron spin. Intermittency in the quantum dot resonance fluorescence allowed us, for the first time, to observe spin quantum jumps in real-time.
Both achievements - highly coherent photons and spin readout - provide the missing link to attempt creation of a small-scale quantum network now
Trapping electrons in a room-temperature microwave Paul trap
We demonstrate trapping of electrons in a millimeter-sized quadrupole Paul
trap driven at 1.6~GHz in a room-temperature ultra-high vacuum setup. Cold
electrons are introduced into the trap by ionization of atomic calcium via
Rydberg states and stay confined by microwave and static electric fields for
several tens of milliseconds. A fraction of these electrons remain trapped
longer and show no measurable loss for measurement times up to a second.
Electronic excitation of the motion reveals secular frequencies which can be
tuned over a range of several tens to hundreds of MHz. Operating a similar
electron Paul trap in a cryogenic environment may provide a platform for
all-electric quantum computing with trapped electron spin qubits.Comment: Version accepted by PR
Surface trap with dc-tunable ion-electrode distance
We describe the design, fabrication, and operation of a novel
surface-electrode Paul trap that produces a radio-frequency-null along the axis
perpendicular to the trap surface. This arrangement enables control of the
vertical trapping potential and consequentially the ion-electrode distance via
dc-electrodes only. We demonstrate confinement of single Ca ions at
heights between m and m above planar copper-coated aluminium
electrodes. We investigate micromotion in the vertical direction and show
cooling of both the planar and vertical motional modes into the ground state.
This trap architecture provides a platform for precision electric-field noise
detection, trapping of vertical ion strings without excess micromotion, and may
have applications for scalable quantum computers with surface ion traps
Changes in electric-field noise due to thermal transformation of a surface ion trap
We aim to illuminate how the microscopic properties of a metal surface map to
its electric-field noise characteristics. In our system, prolonged heat
treatments of a metal film can induce a rise in the magnitude of the
electric-field noise generated by the surface of that film. We refer to this
heat-induced rise in noise magnitude as a thermal transformation. The
underlying physics of this thermal transformation process is explored through a
series of heating, milling, and electron treatments performed on a single
surface ion trap. Between these treatments, Ca ions trapped 70
m above the surface of the metal are used as detectors to monitor the
electric-field noise at frequencies close to 1 MHz. An Auger spectrometer is
used to track changes in the composition of the contaminated metal surface.
With these tools we investigate contaminant deposition, chemical reactions, and
atomic restructuring as possible drivers of thermal transformations. The data
suggest that the observed thermal transformations can be explained by atomic
restructuring at the trap surface. We hypothesize that a rise in local atomic
order increases surface electric-field noise in this system