13 research outputs found
Quantum enhanced optical measurements
L'abstract è presente nell'allegato / the abstract is in the attachmen
Quantum differential ghost microscopy
Quantum correlations become formidable tools for beating classical capacities
of measurement. Preserving these advantages in practical systems, where
experimental imperfections are unavoidable, is a challenge of the utmost
importance. Here we propose and realize a quantum ghost imaging protocol able
to compensate for the detrimental effect of detection noise and losses. This
represents an important improvement as quantum correlations allow low
brightness imaging, desirable for reducing the absorption dose. In particular,
we develop a comprehensive model starting from a ghost imaging scheme
elaborated for bright thermal light, known as differential ghost imaging and
particularly suitable in the relevant case of faint or sparse objects. We
perform the experiment using SPDC light in microscopic configuration. The image
is reconstructed exploiting non-classical intensity correlation rather than
photon pairs detection coincidences. On one side we validate the theoretical
model and on the other we show the applicability of this technique by
reconstructing a biological object with 5 micrometers resolution
Unbiased estimation of an optical loss at the ultimate quantum limit with twin-beams
Loss measurements are at the base of spectroscopy and imaging, thus perme-
ating all the branches of science, from chemistry and biology to physics and
material science. However, quantum mechanics laws set the ultimate limit to the
sensitivity, constrained by the probe mean energy. This can be the main source
of uncertainty, for example when dealing with delicate system such as
biological samples or photosensitive chemicals. It turns out that ordinary
(clas- sical) probe beams, namely with Poissonian photon number distribution,
are fundamentally inadequate to measure small losses with the highest
sensitivity. Conversely, we demonstrate that a quantum-correlated pair of
beams, known as twin-beam state, allows reaching the ultimate sensitivity for
all energy regimes (even less than one photon per mode) with the simplest
measurement strategy. One beam of the pair addresses the sample, while the
second one is used as a reference to compensate both for classical drifts and
for uctuation at the most fundamental quantum level. This scheme is also
absolute and accurate, since it self-compensates for unavoidable instability of
the sources and detectors, which could otherwise lead to strongly biased
results. Moreover, we report the best sensitivity per photon ever achieved in
loss estimation experiments
Photon number correlation for quantum enhanced imaging and sensing
In this review we present the potentialities and the achievements of the use
of non-classical photon number correlations in twin beams (TWB) states for many
applications, ranging from imaging to metrology. Photon number correlations in
the quantum regime are easy to be produced and are rather robust against
unavoidable experimental losses, and noise in some cases, if compared to the
entanglement, where loosing one photon can completely compromise the state and
its exploitable advantage. Here, we will focus on quantum enhanced protocols in
which only phase-insensitive intensity measurements (photon number counting)
are performed, which allow probing transmission/absorption properties of a
system, leading for example to innovative target detection schemes in a strong
background. In this framework, one of the advantages is that the sources
experimentally available emit a wide number of pairwise correlated modes, which
can be intercepted and exploited separately, for example by many pixels of a
camera, providing a parallelism, essential in several applications, like wide
field sub-shot-noise imaging and quantum enhanced ghost imaging. Finally,
non-classical correlation enables new possibilities in quantum radiometry, e.g.
the possibility of absolute calibration of a spatial resolving detector from
the on-off- single photon regime to the linear regime, in the same setup
Quantum Conformance Test
We introduce a protocol addressing the conformance test problem, which
consists in determining whether a process under test conforms to a reference
one. We consider a process to be characterized by the set of end-product it
produces, which is generated according to a given probability distribution. We
formulate the problem in the context of hypothesis testing and consider the
specific case in which the objects can be modeled as pure loss channels. We
demonstrate theoretically that a simple quantum strategy, using readily
available resources and measurement schemes in the form of two-mode squeezed
vacuum and photon-counting, can outperform any classical strategy. We
experimentally implement this protocol, exploiting optical twin beams,
validating our theoretical results, and demonstrating that, in this task, there
is a quantum advantage in a realistic setting
Creation of NV centers in diamond under 155 MeV electron irradiation
Single-crystal diamond substrates presenting a high concentration of
negatively charged nitrogen-vacancy centers (NV-) are on high demand for the
development of optically pumped solid-state sensors such as magnetometers,
thermometers or electrometers. While nitrogen impurities can be easily
incorporated during crystal growth, the creation of vacancies requires further
treatment. Electron irradiation and annealing is often chosen in this context,
offering advantages with respect to irradiation by heavier particles that
negatively affect the crystal lattice structure and consequently the NV-
optical and spin properties. A thorough investigation of electron irradiation
possibilities is needed to optimize the process and improve the sensitivity of
NV-based sensors. In this work we examine the effect of electron irradiation in
a previously unexplored regime: extremely high energy electrons, at 155 MeV. We
develop a simulation model to estimate the concentration of created vacancies
and experimentally demonstrate an increase of NV- concentration by more than 3
orders of magnitude following irradiation of a nitrogen-rich HPHT diamond over
a very large sample volume, which translates into an important gain in
sensitivity. Moreover, we discuss the impact of electron irradiation in this
peculiar regime on other figures of merits relevant for NV sensing, i.e. charge
state conversion efficiency and spin relaxation time. Finally, the effect of
extremely high energy irradiation is compared with the more conventional low
energy irradiation process, employing 200 keV electrons from a transmission
electron microscope, for different substrates and irradiation fluences,
evidencing sixty-fold higher yield of vacancy creation per electron at 155 MeV
Neuronal growth on high-aspect-ratio diamond nanopillar arrays for biosensing applications
Monitoring neuronal activity with simultaneously high spatial and temporal resolution in living cell cultures is crucial to advance understanding of the development and functioning of our brain, and to gain further insights in the origin of brain disorders. While it has been demonstrated that the quantum sensing capabilities of nitrogen-vacancy (NV) centers in diamond allow real time detection of action potentials from large neurons in marine invertebrates, quantum monitoring of mammalian neurons (presenting much smaller dimensions and thus producing much lower signal and requiring higher spatial resolution) has hitherto remained elusive. In this context, diamond nanostructuring can offer the opportunity to boost the diamond platform sensitivity to the required level. However, a comprehensive analysis of the impact of a nanostructured diamond surface on the neuronal viability and growth was lacking. Here, we pattern a single crystal diamond surface with large-scale nanopillar arrays and we successfully demonstrate growth of a network of living and functional primary mouse hippocampal neurons on it. Our study on geometrical parameters reveals preferential growth along the nanopillar grid axes with excellent physical contact between cell membrane and nanopillar apex. Our results suggest that neuron growth can be tailored on diamond nanopillars to realize a nanophotonic quantum sensing platform for wide-field and label-free neuronal activity recording with sub-cellular resolution
Experimental quantum reading with photon counting
The final goal of quantum hypothesis testing is to achieve quantum advantage over all possible classical strategies. In the protocol of quantum reading this advantage is achieved for information retrieval from an optical memory, whose generic cell stores a bit of information in two possible lossy channels. For this protocol, we show, theoretically and experimentally, that quantum advantage is obtained by practical photon-counting measurements combined with a simple maximum-likelihood decision. In particular, we show that this receiver combined with an entangled two-mode squeezed vacuum source is able to outperform any strategy based on statistical mixtures of coherent states for the same mean number of input photons. Our experimental findings demonstrate that quantum entanglement and simple optics are able to enhance the readout of digital data, paving the way to real applications of quantum reading and with potential applications for any other model that is based on the binary discrimination of bosonic loss
Quantum-enhanced pattern recognition
The challenge of pattern recognition is to invoke a strategy that can accurately extract features of a dataset and classify its samples. In realistic scenarios this dataset may be a physical system from which we want to retrieve information, such as in the readout of optical classical memories. The theoretical and experimental development of quantum reading has demonstrated that the readout of optical memories can be dramatically enhanced through the use of quantum resources (namely entangled input-states) over that of the best classical strategies. However, the practicality of this quantum advantage hinges upon the scalability of quantum reading, and up to now its experimental demonstration has been limited to individual cells. In this work, we demonstrate for the first time quantum advantage in the multi-cell problem of pattern recognition. Through experimental realizations of digits from the MNIST handwritten digit dataset, and the application of advanced classical post-processing, we report the use of entangled probe states and photon-counting to achieve quantum advantage in classification error over that achieved with classical resources, confirming that the advantage gained through quantum sensors can be sustained throughout pattern recognition and complex post-processing. This motivates future developments of quantum-enhanced pattern recognition of bosonic-loss within complex domains