170 research outputs found
Phonon-Assisted Two-Photon Interference from Remote Quantum Emitters
Photonic quantum technologies are on the verge offinding applications in everyday life with quantum cryptography andquantum simulators on the horizon. Extensive research has beencarried out to identify suitable quantum emitters and single epitaxialquantum dots have emerged as near-optimal sources of bright, on-demand, highly indistinguishable single photons and entangledphoton-pairs. In order to build up quantum networks, it is essentialto interface remote quantum emitters. However, this is still anoutstanding challenge, as the quantum states of dissimilar“artificialatoms”have to be prepared on-demand with highfidelity and thegenerated photons have to be made indistinguishable in all possibledegrees of freedom. Here, we overcome this major obstacle and show an unprecedented two-photon interference (visibility of 51±5%) from remote strain-tunable GaAs quantum dots emitting on-demand photon-pairs. We achieve this result by exploiting forthefirst time the full potential of a novel phonon-assisted two-photon excitation scheme, which allows for the generation ofhighly indistinguishable (visibility of 71±9%) entangled photon-pairs (fidelity of 90±2%), enables push-button biexciton statepreparation (fidelity of 80±2%) and outperforms conventional resonant two-photon excitation schemes in terms of robustnessagainst environmental decoherence. Our results mark an important milestone for the practical realization of quantum repeatersand complex multiphoton entanglement experiments involving dissimilar artificial atom
Measurement of g-factor tensor in a quantum dot and disentanglement of exciton spins
We perform polarization-resolved magneto-optical measurements on single InAsP
quantum dots embedded in an InP nanowire. In order to determine all elements of
the electron and hole -factor tensors, we measure in magnetic field with
different orientations. The results of these measurements are in good agreement
with a model based on exchange terms and Zeeman interaction. In our experiment,
polarization analysis delivers a powerful tool that not only significantly
increases the precision of the measurements, but also enables us to probe the
exciton spin state evolution in magnetic fields. We propose a disentangling
scheme of heavy-hole exciton spins enabling a measurement of the electron spin
time
Efficient and robust fiber coupling of superconducting single photon detectors
We applied a recently developed fiber coupling technique to superconducting
single photon detectors (SSPDs). As the detector area of SSPDs has to be kept
as small as possible, coupling to an optical fiber has been either inefficient
or unreliable. Etching through the silicon substrate allows fabrication of a
circularly shaped chip which self aligns to the core of a ferrule terminated
fiber in a fiber sleeve. In situ alignment at cryogenic temperatures is
unnecessary and no thermal stress during cooldown, causing misalignment, is
induced. We measured the quantum efficiency of these devices with an attenuated
tunable broadband source. The combination of a lithographically defined chip
and high precision standard telecommunication components yields near unity
coupling efficiency and a system detection efficiency of 34% at a wavelength of
1200 nm. This quantum efficiency measurement is confirmed by an absolute
efficiency measurement using correlated photon pairs (with = 1064 nm)
produced by spontaneous parametric down-conversion. The efficiency obtained via
this method agrees well with the efficiency measured with the attenuated
tunable broadband source
On-chip quantum interference between silicon photon-pair sources
Large-scale integrated quantum photonic technologies1, 2 will require on-chip integration of identical photon sources with reconfigurable waveguide circuits. Relatively complex quantum circuits have been demonstrated already1, 2, 3, 4, 5, 6, 7, but few studies acknowledge the pressing need to integrate photon sources and waveguide circuits together on-chip8, 9. A key step towards such large-scale quantum technologies is the integration of just two individual photon sources within a waveguide circuit, and the demonstration of high-visibility quantum interference between them. Here, we report a silicon-on-insulator device that combines two four-wave mixing sources in an interferometer with a reconfigurable phase shifter. We configured the device to create and manipulate two-colour (non-degenerate) or same-colour (degenerate) path-entangled or path-unentangled photon pairs. We observed up to 100.0 ± 0.4% visibility quantum interference on-chip, and up to 95 ± 4% off-chip. Our device removes the need for external photon sources, provides a path to increasing the complexity of quantum photonic circuits and is a first step towards fully integrated quantum technologies
Surround-gated vertical nanowire quantum dots
We report voltage dependent photoluminescence experiments on single indium arsenide phosphide (InAsP) quantum dots embedded in vertical surround-gated indium phosphide (InP) nanowires. We show that by tuning the gate voltage, we can access different quantum dot charge states. We study the anisotropic exchange splitting by polarization analysis, and identify the neutral and singly charged exciton. These results are important for spin addressability in a charge tunable nanowire quantum dot
Correlated photon-pair generation in a periodically poled MgO doped stoichiometric lithium tantalate reverse proton exchanged waveguide
We demonstrate photon-pair generation in a reverse proton exchanged waveguide
fabricated on a periodically poled magnesium doped stoichiometric lithium
tantalate substrate. Detected pairs are generated via a cascaded second order
nonlinear process where a pump laser at wavelength of 1.55 m is first
doubled in frequency by second harmonic generation and subsequently
downconverted around the same spectral region. Pairs are detected at a rate of
42 per second with a coincidence to accidental ratio of 0.7. This cascaded pair
generation process is similar to four-wave-mixing where two pump photons
annihilate and create a correlated photon pair
High-Performance Photon Number Resolving Detectors for 850-950 nm wavelengths
Since their first demonstration in 2001, superconducting-nanowire
single-photon detectors have witnessed two decades of great developments.
SNSPDs are the detector of choice in most modern quantum optics experiments and
are slowly finding their way into other photon starved fields of optics. Until
now, however, in nearly all experiments SNSPDs were used as binary detectors,
meaning they can only distinguish between 0 and more than 1 photons and photon
number information is lost. Recent research works have demonstrated proof of
principle photon number resolving (PNR) SNSPDs counting 2 to 5 photons. The
photon-number-resolving capability is highly demanded in various quantum-optics
experiments, including HOM interference, photonic quantum computing, quantum
communication, and non Gaussian quantum state preparation. In particular, PNR
detectors at the wavelength range of 850 to 950 nm are of great interest due to
the availability of high quality semiconductor quantum dots and
high-performance Cesium-based quantum memories. In this paper, we demonstrate
NbTiN based SNSPDs with over 94 percent system detection efficiency, sub 11 ps
timing jitter for one photon, and sub 7 ps for two photon. More importantly,
our detectors resolve up to 7 photons using conventional cryogenic electric
readout circuitry. Through theoretical analysis, we show that the current PNR
performance of our detectors can still be further improved by improving the
signal to noise ratio and bandwidth of our readout circuitry. Our results are
promising for the future of optical quantum computing and quantum
communication
Impedance model for the polarization-dependent optical absorption of superconducting single-photon detectors
We measured the single-photon detection efficiency of NbN superconducting
single photon detectors as a function of the polarization state of the incident
light for different wavelengths in the range from 488 nm to 1550 nm. The
polarization contrast varies from ~5% at 488 nm to ~30% at 1550 nm, in good
agreement with numerical calculations. We use an optical-impedance model to
describe the absorption for polarization parallel to the wires of the detector.
For lossy NbN films, the absorption can be kept constant by keeping the product
of layer thickness and filling factor constant. As a consequence, we find that
the maximum possible absorption is independent of filling factor. By
illuminating the detector through the substrate, an absorption efficiency of
~70% can be reached for a detector on Si or GaAs, without the need for an
optical cavity.Comment: 15 pages, 5 figures, submitted to Journal of Applied Physic
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