Abstract As an important quantum resource, optical cat state is successfully prepared and applied in quantum information science. It is shown that optical quantum states carrying orbital angular momentum (OAM) have wide applications in quantum communication and quantum precision measurement. Here, optical cat states carrying OAM are experimentally prepared with topological charges = 0, +1, +2, +4 by changing the wavefront of the photon‐subtracted squeezed vacuum state with a combination of quarter‐wave plate and q‐plate. To verify the prepared cat states, both Wigner functions and topological charges of OAM are measured. It is shown that the fidelities and amplitudes of optical cat states carrying OAM decrease slightly with the increase of topological charges of OAM, although the spatial size of the optical beam is increased. These results present a new kind of optical cat state carrying OAM, which has potential applications in quantum precision measurement.
Abstract As an important quantum resource, optical cat state is successfully prepared and applied in quantum information science. It is shown that optical quantum states carrying orbital angular momentum (OAM) have wide applications in quantum communication and quantum precision measurement. Here, optical cat states carrying OAM are experimentally prepared with topological charges = 0, +1, +2, +4 by changing the wavefront of the photon‐subtracted squeezed vacuum state with a combination of quarter‐wave plate and q‐plate. To verify the prepared cat states, both Wigner functions and topological charges of OAM are measured. It is shown that the fidelities and amplitudes of optical cat states carrying OAM decrease slightly with the increase of topological charges of OAM, although the spatial size of the optical beam is increased. These results present a new kind of optical cat state carrying OAM, which has potential applications in quantum precision measurement.
A squeezed state is a key quantum resource for quantum information processing and quantum metrology. It is essential to extend the dimension of the squeezed state for spatially multiplexed large-capacity quantum communication and quantum precision measurements. Here, we report the experimental preparation of a picosecond pulsed squeezed state carrying orbital angular momentum (OAM). By modulating bright pulsed squeezed light with a spatial light modulator, we generate a squeezed state with Laguerre-Gaussian distribution, whose topological charges are up to l = 20 and squeezed noise is 1.22 dB below the shot noise level. The presented bright picosecond pulsed squeezed light carrying high-order OAM provides promising resources for high-dimensional quantum information processing.
ABSTRACT The quantum measurement scheme exhibits significant advantages in precision measurement, due to super‐sensitivity. In particular, the multi‐photon NOON states realized via path or polarization degrees of freedom have been successfully validated in various phase measurement experiments. Orbital angular momentum (OAM), another important photonic degree of freedom, has also shown great potential for angular measurement. Combining the NOON state with OAM is expected to demonstrate quantum advantages in such measurements. Here we experimentally generate a three‐photon NOON state based on OAM for the first time, and apply it to super‐sensitive angular measurement. By utilizing a NOON state with a topological charge as high as , we have achieved a precision beyond the standard quantum limit. Through the reduction of angle uncertainty, a sensitivity reaching approximately 82% of the ideal Heisenberg limit is achieved. These results establish the practical utility of OAM‐enhanced NOON states in advancing angular metrology. Our experiments indicate that increasing either the topological charge or the photon number can substantially improve angular measurement accuracy. Importantly, the proposed scheme exhibits excellent scalability in key parameters, underscoring its potential for high‐precision angle‐sensing applications.
Light orbital angular momentum (OAM) has been recognized as a new promising resource for classical and quantum information applications. In contrast to the spin angular momentum, the OAM is an inherently multidimensional. Thus, the information can be encoded in the higher-dimensional OAM alphabets. Recently, Marrucci et al. have invented a new device named q-plate (QP), made of liquid crystal cell patterned in such a way to introduce a topological charge q at the transverse plane, which is able to generate a well-defined values of photon OAM. My research has been aimed at investigating the physics of the QP, of the optical fields that it generates and of its possible applications for optical communication and quantum information. We studied both theoretically and experimentally a novel set of non-orthogonal but over-complete paraxial modes, named Hypergeometric-Gaussian modes, that is typically associated with OAM-carrying optical fields. We have also found the light propagation kernel inside the QP and we have shown analytically that if small losses due to reflection, absorption, and scattering are neglected, the QP can convert the photon spin into OAM with up to 100 \% efficiency. We implemented a technique to control the QP optical retardation by tuning the QP temperature. At the optimal temperature, the QP can generate a beam with up to 97\% efficiency. Moreover, the OAM state generated by QP can be rotated easily in the 2D OAM Hilbert space by proper manipulation of the input polarization state, a fact which opens a new way of beam shape controlling in MHz scale. We also performed a novel way to encode and read two bits information on the 4D OAM space by using only one QP. Finally, we experimentally demonstrated the transfer of quantum information from spin to OAM and vice versa, including the case of bi-photon states having quantum correlations. Furthermore, by exploiting these quantum information transfer devices, we demonstrated the Hong-Ou-Mandel effect and the optimal quantum cloning with OAM-carrying photons.
Abstract Electromagnetic waves have both spin momentum and orbital angular momentum (OAM). Light carrying OAM has broad applications in micro-particle manipulation, high-precision optical metrology, and potential high-capacity optical communications. In the concept of quantum information, a photon encoded with information in its OAM degree of freedom enables quantum networks to carry much more information and increase their channel capacity greatly compared with those of current technology because of the inherent infinite dimensions for OAM. Quantum memories are indispensable to construct quantum networks. Storing OAM states has attracted considerable attention recently, and many important advances in this direction have been achieved during the past few years. Here we review recent experimental realizations of quantum memories using OAM states, including OAM qubits and qutrits at true single photon level, OAM states entangled in a two-dimensional or a high-dimensional space, hyperentanglement and hybrid entanglement consisting of OAM and other degree of freedom in a physical system. We believe that all achievements described here are very helpful to study quantum information encoded in a high-dimensional space.
The beam with orbital angular momentum is a present domestic and foreign research key direction. Its application and development will bring the profound influence in the optical communications field. At the same time, light's orbital angular momentum promises potential applications in both classical and quantum optical communication. The research progress of the beam with orbital angular momentum and encoding information as light's OAM for free-space optical communication were reviewed in this article, the existing design method, mechanism and description methods of encoding information as light's OAM were discussed. In quantum communication, qudits can be encoded in photons using their OAM for creating high-dimensional entanglement based on entangled photon pairs from SPDC. In this paper, light's OAM is used as information carrier for classical and quantum communication, which is promising to ensures the security of atmospheric laser communication, improves the density and precision of information transmission. It is apparent that an efficient way to measure the orbital angular momentum of individual photons and light beams with good efficiency would be of potentially great importance for optical communications and quantum information. In view of the above, the measurements of orbital angular momentum of individual photons and light beams are analyzed and discussed in detail.
Photons are an ideal candidate for encoding both classical and quantum information. Besides spin angular momentum associated with circular polarization, single photon can also carry other fundamentally new degree of freedom of orbital angular momentum related to the spiral phase structure of light. The key significance of orbital angular momentum lies in its potential in realizing a high-dimensional Hilbert space and in encoding a high-dimensional quantum information. Since Allen et al. [Allen L, Beijersbergen M W, Spreeuw R J C, Woerdman J P 1992 Phys. Rev. A 45 8185] recognized the physical reality of photon orbital angular momentum in 1992, rapidly growing interest has been aroused in orbital angular momentum (OAM) from both classical and quantum points of view. Here we present an overall review on the high-order orbital angular momentum of photon, including its preparation and manipulation based on some specific techniques and also its applications. The spatial light modulator is a commercial device that has been widely employed to generate the OAM beams. We make and identify the optical OAM superposition with very high quantum numbers up to l=360. Recently, the metallic spiral phase mirrors were also developed to produce high-order OAM beams up to l=5050. In addition, the Q-plates made of anisotropic and inhomogeneous liquid crystals were invented to generate high-order OAM beams in a polarization-controllable manner, and the OAM superposition of l=± 50 were achieved. Owing to high rotational symmetry, these high OAM beams have been found to have more and more important applications in the fields of high-sensitivity sensing and high-precision measurements. Two fascinating examples are discussed in detail. The first example is that the research group led by Prof. Zeilinger has prepared and observed the quantum entanglement of high orbital angular momenta up to l=±300 by the technique of polarization-OAM entanglement swapping, and they demonstrated that the angular resolution could be significantly improved by a factor of l. Their result was the first step for entangling and twisting even macroscopic, spatially separated objects in two different directions. The second example is that the research group led by Prof. Padgett has demonstrated an elegant experiment of rotational Doppler effects for visible light with l=±20 OAM superposition. They showed that a spinning object with an optically rough surface might induce a Doppler effect in light reflected from the direction parallel to the rotation axis, and the frequency shift was proportional to both the disk's angular speed and the optical OAM. The potential applications in noncontact measurement of angular speed and in significant improvement of angular resolution for remote sensing will be particularly fascinating.