In this work a quantum imaging setup based on undetected squeezed photons is employed for metrological applications such as sensitive phase measurement and quantum imaging. In spite of the traditional quantum imaging with undetected photons, introduced by A. Zeilinger et. al, the proposed setup is equipped by a homodyne detection and also the brightness of the quantum light is enhanced by an optical parametric oscillator (OPO). Introducing OPO may be diminish the validity of the low gain approximation, so a theoretical approach beyond this approximation is introduced. Due to the resource of squeezing, the results reveal the higher amount of signal to noise ratio, as a measure of image quality and phase-measurement accuracy. Accordingly, an imaging protocol is introduced to suppress the background noises, effectively. Interestingly, This protocol provides a way to extract the image information which is encoded in the quantum fluctuation (noise). Therefore, non-disruptive imaging is achievable, which is noteworthy subject in the field of bio-imaging of sensitive and low damage threshold living cells.
In this work a quantum imaging setup based on undetected squeezed photons is employed for metrological applications such as sensitive phase measurement and quantum imaging. In spite of the traditional quantum imaging with undetected photons, introduced by A. Zeilinger et. al, the proposed setup is equipped by a homodyne detection and also the brightness of the quantum light is enhanced by an optical parametric oscillator (OPO). Introducing OPO may be diminish the validity of the low gain approximation, so a theoretical approach beyond this approximation is introduced. Due to the resource of squeezing, the results reveal the higher amount of signal to noise ratio, as a measure of image quality and phase-measurement accuracy. Accordingly, an imaging protocol is introduced to suppress the background noises, effectively. Interestingly, This protocol provides a way to extract the image information which is encoded in the quantum fluctuation (noise). Therefore, non-disruptive imaging is achievable, which is noteworthy subject in the field of bio-imaging of sensitive and low damage threshold living cells.
In this work a quantum imaging setup based on undetected squeezed photons is employed for metrological applications such as sensitive phase measurement and quantum imaging. Unlike traditional quantum imaging with undetected photons, as introduced by A. Zeilinger et al., the proposed setup incorporates a homodyne detection system and enhances the brightness of the quantum light using optical parametric oscillators (OPOs). The inclusion of OPOs may challenge the validity of the low-gain approximation, necessitating the development of a new theoretical framework that extends beyond this approximation. The results demonstrate a higher signal-to-noise ratio, which serves as a key metric for both image quality and phase-measurement accuracy. Furthermore, an imaging protocol is introduced to effectively suppress background noise. Notably, this protocol enables the extraction of image information encoded in quantum fluctuations (noise), paving the way for non-disruptive imaging. This is particularly significant in the field of bio-imaging, since the object (a sensitive living cell) is interrogated by longer-wavelength idler light while detection is applied at optical frequency in which the sensors are less noisy and has more quantum efficiency.
Quantum-enhanced metrology techniques offer ultra-precise timekeeping, allowing for breakthroughs in navigation systems, global positioning, medical and Biological imaging. Quantum metrology, a core application of quantum technologies, leverages non-classical states of light (such as entanglement and squeezing) to enhance measurement precision, sensitivity, and resolution beyond the classical limits, particularly the shot-noise limit. Its application to bio imaging and microscopy offers significant advantages for studying delicate biological specimens, which are often susceptible to damage from the intense light typically required by conventional high-resolution methods. The abstract highlights the potential of quantum properties of light to revolutionize bio imaging by providing a non-invasive, highly sensitive, and high-resolution platform for observing biological processes at fundamental scales.
Abstract Among the known resources of quantum metrology, one of the most practical and efficient is squeezing. Squeezed states of atoms and light improve the sensing of the phase, magnetic field, polarization, mechanical displacement. They promise to considerably increase signal-to-noise ratio in imaging and spectroscopy, and are already used in real-life gravitational-wave detectors. But despite being more robust than other states, they are still very fragile, which narrows the scope of their application. In particular, squeezed states are useless in measurements where the detection is inefficient or the noise is high. Here, we experimentally demonstrate a remedy against loss and noise: strong noiseless amplification before detection. This way, we achieve loss-tolerant operation of an interferometer fed with squeezed and coherent light. With only 50% detection efficiency and with noise exceeding the level of squeezed light more than 50 times, we overcome the shot-noise limit by 6 dB. Sub-shot-noise phase sensitivity survives up to 87% loss. Application of this technique to other types of optical sensing and imaging promises a full use of quantum resources in these fields.
Quantum interference with undetected photons has gained significant attention in the past ten years due to its potential to decouple the probing and the detection of an active sensing system. The technique is based on correlated photon pairs: one photon interacts with the analyte, and the signature of the interaction is stored in its correlated counterpart. The probing photon remains undetected, while the other photon is measured. When the photons are highly non-degenerate, the spectral separation of the probing and detected photons offers significant advantages in terms of ease of operation and enhanced sensitivity, enabling more precise measurements and analysis with respect to other sensing techniques. This possibility enables a wide range of applications, particularly in fields such as imaging, spectroscopy, and optical coherence tomography, among others. This thesis describes experiments for imaging and sensing based on undetected photons, both in a free-space optical setup and in an integrated photonic circuit. The free-space configuration was used to perform undetected three-dimensional imaging reconstruction of diffusive targets. This validation of imaging with undetected photons paves the way to further development to in vivo biomedical imaging, covert imaging, and remote sensing. On the other hand, the integrated configuration overcomes the limitation of alignment tolerance and scalability of a free-space optical setup, enabling the development of integrated sensors based on undetected photons.
Without light, there would be no sight. Light acts as a probe in various measurement techniques ranging from imaging to spectroscopy, from small scale cantilever displace- ment measurement in atomic force microscopy to large scale mirror motion in interfer- ometry, light detection and ranging (LIDAR) and many other fields. As the light probe intensity rises, it not only allows reducing the background noise effect, but it also aids precision to the measurement by reducing the photon noise (shot-noise) contribution. However, increasing intensity beyond certain threshold level is not always advantageous for ultra sensitive measurements. For example in the detection of gravitational waves, the current power circulating in the large scale interferometers can not be increased further without introducing other noise sources like thermal effects on the mirrors, un- wanted scattered photons, and back action due to radiation pressure. In the imaging of delicate photo sensitive sample, high power can causes cell damage or it may lead to disturb the regular process under investigation, viz. favouring certain biochemical reaction, which do not correspond to natural in vitro behaviour. At low intensity, pho- ton noise is an important concern and quantum states of light with correlated photon fluctuation can ideally represent a fruitful way to build specific measurement strategies to surpass the limitation of standard approach based on classical light sources, offering an avenue of solutions for ultra sensitive measurements. This thesis work focuses on two application of quantum enhanced measurement strate- gies. The first part of the thesis work has been dedicated to the realization of the first wide-field microscope with Sub Shot Noise (SSN) sensitivity. This is based on the ex- ploitation of quantum correlations in the Squeezed Vacuum state. In the second part, the investigations have made on the role of the quantum correlated beams in an unusual interferometric scheme, in which two identical optical interferometers are subject to the same phase fluctuation. The scheme, in the classical regime, has been already imple- mented in a large scale experiment devoted to the search of possible quantum gravity (QG) effects at Fermilab.
The use of optical sensing for in vivo applications is compelling, since it offers the advantages of non-invasiveness, non-ionizing radiation, and real-time monitoring. However, the signal-to-noise ratio (SNR) of the optical signal deteriorates dramatically as the biological tissue increases. Although increasing laser power can improve the SNR, intense lasers can severely disturb biological processes and viability. Quantum sensing with bright squeezed light can make the measurement sensitivity break through the quantum noise limit under weak laser conditions. A bright squeezed light source is demonstrated to avoid the deterioration of SNR and biological damage, which integrates an external cavity frequency-doubled laser, a semi-monolithic standing cavity with periodically poled titanyl phosphate (PPKTP), and a balanced homodyne detector (BHD) assembled on a dedicated breadboard. With the rational design of the mechanical elements, the optical layout, and the feedback control equipment, a maximum non-classical noise reduction of −10.7 ± 0.2 dB is observed. The average squeeze of −10 ± 0.2 dB in continuous operation for 60 min is demonstrated. Finally, the intracavity loss of degenerate optical parametric amplifier (DOPA) and the initial bright squeezed light can be calculated to be 0.0021 and −15.5 ± 0.2 dB, respectively. Through the above experimental and theoretical analysis, the direction of improving bright squeeze level is pointed out.