Color centres in diamond represent a very interesting system for realizing single photon emitters, even at room temperature, in particular are attracting an ever-growing interest in quantum optics, quantum information and quantum sensing, due to their appealing photo-physical properties combined with ease of access and manipulation in a solid state system characterized by high transparency and structural stability. Literally hundreds of optically active color centers can be created and controlled in the diamond matrix, to be employed either as bright and stable single-photon sources or individual spin systems with optical readout, with record performances even at room temperature. In concurrence with the remarkable results obtained at the state of the art on the exploitation of the unique properties of the negatively-charged nitrogen-vacancy complex (NV), new and appealing color centers are continuously being discovered and characterized. In the present contribution, the most recent results obtained by a collaboration among the Italian National Institutes of Metrologic Research (INRiM), the University of Torino and the Italian National Institutes of Nuclear Physics (INFN) will be overviewed and critically assessed in their future perspectives.
Properties of quantum light represent a tool for overcoming limits of classical optics. Several experiments have demonstrated this advantage ranging from quantum enhanced imaging to quantum illumination. In this work, experimental demonstration of quantum-enhanced resolution in confocal fluorescence microscopy will be presented. This is achieved by exploiting the non-classical photon statistics of fluorescence emission of single nitrogen-vacancy (NV) color centers in diamond. By developing a general model of super-resolution based on the direct sampling of the kth-order autocorrelation function of the photoluminescence signal, we show the possibility to resolve, in principle, arbitrarily close emitting centers. Finally, possible applications of NV-based fluorescent nanodiamonds in biosensing and future developments will be presented.
We analyze in detail a system of two interferometers aimed at the detection of extremely faint phase fluctuations. The idea behind is that a correlated phase-signal like the one predicted by some phenomenological theory of Quantum Gravity (QG) could emerge by correlating the output ports of the interferometers, even when in the single interferometer it confounds with the background. We demonstrated that injecting quantum light in the free ports of the interferometers can reduce the photon noise of the system beyond the shot-noise, enhancing the resolution in the phase-correlation estimation. Our results confirm the benefit of using squeezed beams together with strong coherent beams in interferometry, even in this correlated case. On the other hand, our results concerning the possible use of photon number entanglement in twin beam state pave the way to interesting and probably unexplored areas of application of bipartite entanglement and, in particular, the possibility of reaching surprising uncertainty reduction exploiting new interferometric configurations, as in the case of the system described here.
We present two recent results achieved in INRIM laboratories paving the way for next future commercial use of quantum imaging techniques. The first exploits non-classical photon statistics of single nitrogen-vacancy color centers in diamond for realising super-resolution. A little more in detail we demonstrate that the measurement of high order correlation functions allows overcoming Abbe limit. The second exploits ghost imaging in a specific case of practical interest, i.e. in measuring magnetic structures in garnets.
Single-photon sources (SPS) play a key-role in many applications, spanning from quantum metrology, to quantum information and to the foundations of quantum mechanics. Even if an ideal SPS (i. e. emitting indistinguishable, ”on-demand” single photons, at an arbitrarily fast repetition rate) is far to be realized due to real-world deviations from the ideality, much effort is currently devoted to improving the performance of real sources. With regards to the emission probability, it appears natural to employ sources that are in principle deterministic in the single- photon emission (single quantum emitters such as single atoms, ions, molecules, quantum dots, or color centers in diamond) as opposed to probabilistic ones (usually heralded SPS based on parametric down-conversion). We present an overview of our latest results concerning a work-in-progress NIR pulsed single photon source based on single quantum emitters (color centers in diamond) exploiting recently reported centers. They are particularly interesting because of the narrow emission line (tipically less than 5 nm), the shorter excited state lifetime with respect to NV centres (1 - 2 ns compared to 12 ns, allowing a ten-fold photon emission rate upon saturation) and the polarized emission.
With the recent progresses in quantum technologies, single photon sources have gained a primary relevance. Here we present a heralded single photon source characterized by an extremely low level of noise photons, realized by exploiting low-jitter electronics and detectors and fast custom-made electronics used to control an optical shutter (a LiNbO<sub>3</sub> waveguide optical switch) at the output of the source. This single photon source showed a second-order autocorrelation function <i>g</i><sup>(2)</sup>(0) = 0:005(7), and an <i>Output Noise Factor</i> (defined as the ratio of noise photons to total photons at the source output) of 0:25(1)%, among the best ever achieved.
Quantum Key Distribution together with its intrinsic security represent the more promising technology to meet the challenging requests of novel generation communication protocols. Beyond its relevant commercial interests, QKD is currently and deeply investigated in research fields as quantum information and quantum mechanics foundations, in order to push over the limits of the actual resources needed to ensure the security of quantum communication. Aim of the paper is to contribute to this open debate presenting our last experimental implementations concerning two novel quantum cryptographic schemes which do not require some of the most widely accepted conditions for realizing QKD. The first is Goldenberg-Vaidman<sup>1,2</sup> protocol, in which even if only orthogonal states (that in principle can be cloned without altering the quantum state) are used, any eavesdropping attempt is detectable. The second is N09<sup>3</sup> protocol which, being based on the quantum counterfactual effect, does not even require any actual photon transmission in the quantum channel between the parties for the communication. The good agreement between theoretical predictions and experimental results represent a proof of principle of the experimental feasibility of the novel protocols.
In this proceedings we will present a research project financed by Piedmont regional government (Italy) and finalized to
the realization and commercialization of functional devices for cellular bio-sensing based on diamond. Partners of the
project are: Crisel Instruments, Torino University, Torino Polytechnic, INRIM, Politronica, Bionica Tech, Ulm
Here the main features of the final devices will be briefly summarized.
We envisage an active diamond-based cellular substrate that can simultaneously stimulate and detect a variety of signals
(chemical, optical, electrical) to and from neuroendocrine cells, in a fully biocompatible environment for the cellular
system under test. Such a device can be realized by fully exploiting the peculiar properties of diamond: optical
transparency, biocompatibility, chemical inertness, accessibility to a conductive graphite-like phase; properties that will
be further explored and tested during the project.
Since, in general, non-orthogonal states cannot be cloned, any eavesdropping attempt in a Quantum Communication
scheme using non-orthogonal states as carriers of information introduces some errors in the transmission,
leading to the possibility of detecting the spy. Usually, orthogonal states are not used in Quantum Cryptography
schemes since they can be faithfully cloned without altering the transmitted data. Nevertheless, L. Goldberg
and L. Vaidman [Phys. Rev. Lett. 75 (7), pp. 12391243, 1995] proposed a protocol in which, even if the data
exchange is realized using two orthogonal states, any attempt to eavesdrop is detectable by the legal users. In
this scheme the orthogonal states are superpositions of two localized wave packets which travel along separate
channels, i.e. two different paths inside a balanced Mach-Zehnder interferometer. Here we present an experiment
realizing this scheme.
In this paper we review our recent works on the generation of different Bell states within the lineshape of
parametric down-conversion (SPDC) and their possible applications. Indeed, for polarization-entangled two-photon
states produced via SPDC, the frequency-angular lineshape allowed by phase matching is considered. It
is shown that there are always different Bell states generated for different mismatch values within the natural
bandwidth. Consideration is made for two different methods of polarization entanglement preparation, based on
type-II SPDC and on SPDC in two type-I crystals producing orthogonally polarized photon pairs. Different Bell
states can be filtered out by either frequency selection or angular selection, or both. Our theoretical calculations
are confirmed by a series of experiments, performed for the two above-mentioned ways of producing polarization-entangled
photon pairs and with two kinds of measurements: frequency-selective and angular-selective. Finally, we mention possible application to quantum communication with fibers.