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Quantum readout techniques and technologies

Periodic Reporting for period 1 - QUARTET (Quantum readout techniques and technologies)

Reporting period: 2019-11-01 to 2020-10-31

Quantum information is today a mature cutting-edge science that is ready to develop next-generation quantum technologies for the benefit of the wider society. Among its potential future applications, some of the most important will be related to the storage, analysis and manipulation of classical data. Data are in fact becoming so large and complex to make traditional processing techniques completely inadequate, with crucial challenges for important areas like business, health care, and societal security. In line with these increasingly pressing issues, the general aim of this project is to exploit the laws of quantum mechanics and the tools of quantum information to develop new powerful methods for the retrieval and recognition of classical data from physical systems. More precisely, we aim at showing a substantial quantum-enhancement in several tasks, including:

-The readout of classical data from optical digital memories (quantum reading)
-The recognition of classical patterns (quantum pattern recognition)
-The optical measurement of concentration in fragile biomedical samples (quantum bio-probing)
-The microwave detection of target objects (microwave quantum illumination or quantum radar)

These objectives are realized starting from the optimization of a general theoretical model at their basis: quantum hypothesis testing. This basic model is then gradually developed into technical studies and proof-of-principle experimental demonstrations of these quantum technologies.

Efficiently reading bits of data with just a few photons means that new kinds of organic memories and photodegradable materials could be considered. This can be particularly useful at high frequencies, where dye-based supports become extremely photosensitive. The basic working mechanism might be developed into more efficient technologies for data storage/retrieval, with increased transfer rates and capacities. Thanks to the superior performance at very low energies, quantum reading and pattern recognition might have long-term applications in biology and medicine. The potential is for a fully non-invasive probing of fragile biological samples or human tissues, e.g. for recognizing patterns associated with bacterial growths or cancerous cells. These patterns could be identified by non-invasive quantum-correlated light, whereas classical light would either damage/destroy the samples or be unable to extract meaningful information. Such results could lead to future non-invasive techniques for biomedical imaging. The development of a short-range quantum radar can have potential applications in terms of continuous-running low-power environmental scanning, both for safety and security.
The consortium has produced many theoretical results. In a recent work, we have
established the ultimate limits for the adaptive discrimination of an arbitrary number of
quantum channels, also showing how these limits can be achieved for channels with suitable
symmetries. In this paper and other two works, we have investigated and
established the optimal performances that are achievable in the adaptive discrimination
of amplitude damping channels, which describe bosonic lossy channels when the input state
is truncated to one photon. In a series of other papers,
we have shown that “cheap” quantum states can be engineered to achieve quantum advantage
in discriminating lossy channels, with applications to target detection, and biological sensing.

We have realized a first experiment on quantum reading, where the readout of
information from a memory cell was enhanced by the use of entangled light. We also showed,
theoretically and experimentally, that this quantum advantage can be obtained by using
practical photo-detection strategies. In theoretical studies, we have discovered the optimal
yet practical receiver for quantum reading and we have generalized the protocol to
a more general position-based version, which is a basic form of pattern recognition with bosonic channels.
We have also showed that low-energetic quantum states of light are able to outperform classical
sources in performing non-invasive detection and identification of bacteria.

We have progressed in the experimental realization of Josephson amplifiers and performed a
proof-of-principle demonstration of the protocol of microwave quantum illumination where a
target was detected at room temperature at the distance of 1 meter. We have also
started the design of practical receivers for quantum illumination which should lead to
improved next implementations of this protocol.

A number of other results were obtained in connection with the highlights described above
that will generally contribute to advance the are of bosonic quantum sensing, both theoretically
and experimentally.
By the end of the project, we expect to advance the areas of quantum hypothesis testing
and quantum sensing in several aspects. From a theoretical point of view, we will better
clarify the ultimate limits and performances acheivable in the problem of quantum channel
discrimination, which is at the basis of several quantum technological protocols, such as
quantum reading and quantum illumination. We will extend this basic theory to cover more advanced
formulations, so to design protocols for quantum-enhanced decoding of barcodes and classification
of images. From the experimental point of view, we will realize our theoretical ideas in the lab
by performing experiments which demonstrate the superiority of quantum sources
for the retrieval of information from physical systems. We will show how to use
quantum entanglement and other quantum properties (e.g. squeezing) to better retrieve
data from prototypes of optical memories under conditions of small input energy.
We aim at showing a similar quantum advantage for the detection and classification
of fragile bacteria in samples, and for scanning low-reflectivity targets in very noisy environments.

Potential long-term impact:

1) Quantum reading of data: Efficiently reading bits of data with just a few photons means that new kinds of organic memories
and photodegradable materials could be considered. This can be particularly useful at high frequencies,
where dye-based supports become extremely photosensitive. In the long term, the basic working mechanism
might be developed into more efficient technologies for data storage/retrieval, with increased transfer rates.

2) Quantum pattern recognition and quantum bio-probing: The potential is for a fully non-invasive probing
of fragile biological samples or human tissues, e.g. for recognizing patterns associated with bacterial
growths or cancerous cells. These patterns could be identified by non-invasive quantum-correlated light,
whereas classical light would either damage/destroy the samples or be unable to extract meaningful information.
Such results could lead to future non-invasive techniques for biomedical imaging.

3) Quantum radar/scanner: The development of a short-range quantum radar can have potential applications in
terms of continuous-running low-power environmental scanning. This might be used for safety applications,
e.g. as a proximity sensor for obstacle detection, and for security applications, e.g. as a scanner and
surveillance tool in certain densely-populated environments such as airports.
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