= APPENDIX: QUANTUM BASED TECHNOLOGIES =
B. QUANTUM OPTICAL MEASUREMENT TECHNOLOGIES
PHYSICAL APPROACH AND PERSPECTIVE
The success in quantum science and engineering has created several extremely valuable optical tools that operate exclusively under the rules of quantum mechanics and offering practical optical measurement and characterization techniques (quantum optical metrology) that has clear advantages over existing technologies.
The main step in the development of quantum correlation and quantum entanglement tools was a practical design of ultra-bright sources of correlated photons and development of novel principles of entangled states engineering. This also includes entangled states of higher dimensionality and entangled quantum states demonstrating simultaneous entanglement in several pairs of quantum variables (hyper-entanglement).
STATE OF THE ART AND PRACTICAL EXAMPLES (NOVEMBER 2004)
- Calibration of single-photon detectors without any need for using traditional blackbody radiation sources. This unique possibility of self-referencing present in the optical system that is distributed in space-time is the main advantage of quantum correlation and entanglement.
- The fact that SPDC is initiated by vacuum fluctuations serves as a universal and independent reference for measuring the optical radiation brightness (radiance). Gives the possibility of accurately measuring the infrared radiation brightness without the need of using very noisy and low sensitivity infrared detectors.
- Development of periodically poled nonlinear structures has opened the road for practical implementation of sources with high intensity of entangled-photon flux and with ultra high spectral bandwidth for biomedical coherence imaging.
- Recent demonstrations have shown the possibilities for multi-photon interferometry beyond the classical limit.
- It has been shown that weak field homodyning could yield enhanced resolution in phase detection.
- First experimental implementations of quantum ellipsometry indicated the high potential of quantum polarization measurement.
- The basic physical principles of optical coherence tomography with dispersion cancellation using frequency entangled photon pairs for sub-micron biomedical imaging has been demonstrated in model environment.
- The use of quantum correlation led to the design of a new technique for characterizing chromatic dispersion in fibers.
- The intrinsically quantum interplay between the polarization and frequency entanglement in SPDS gave rise to a polarization mode dispersion measurement technique that provides an order of magnitude enhancement in the resolution.
FUTURE DIRECTIONS AND CHALLENGES
The need for ultra-high resolution non-invasive optical measurement is one of the novel challenges with modern biophotonics and nanotechnology moving towards creation and manipulation of nanoscale features. The existing characterization techniques are intrinsically invasive and often change the physical and chemical structure after its characterization.
Optical technologies can provide the non-invasive character of evaluation and satisfy the constraint of measuring dimensions that are smaller than the wavelength of light when a broad optical spectrum is employed.
SHORT-TERM GOALS (NEXT 3-5 YEARS)
- Evaluation and characterization of quantum states entangled in polarization, frequency, and direction of propagation.
- Engineering and technological design of hyper-entangled quantum states utilizing artificially created complex one- and two-dimensional periodically modulated nonlinear structures.
- The design of states with a super-broadband spectrum and with a high degree of polarization entanglement for biomedical applications and for quantum spectroscopic ellipsometry.
- Developing generators of quantum states of light of interest to high-resolution interferometry or lithography such as "NOON" states using linear optics.
- The quantum enhanced resolution in phase measurement using entangled multi-photon states and weak field homodyning.
- Developing multi-spectral quantum ellipsometry for characterization of non-isotropic samples of polymers, organic materials, biological objects, and nanoscale semiconductor patterns.
- Developing quantum optical coherence tomography using dispersion cancellation effect to reach sub-micron axial resolution in biological tissue.
- Developing quantum super-resolution microscopy with polarization-entangled photons and with a two-photon single atom laser.
- Developing compact fiber-based sub-systems for practical demonstration of quantum-optical measurement schemes and fiber sensors.
- Developing integrated solid-state quantum measurement tools and sensors by manipulating photonic qubits using nonlinear-optical and semiconductor materials.
LONG-TERM GOALS (2010 AND BEYOND)
Development of integrated entangled-photon circuits for specific quantum optical metrology applications that are ready for incorporation in technological processes.
 A. V. Sergienko and G. S. Jaeger Quantum Information Processing and Precise Optical measurement with Entangled-Photon Pairs, Contemporary Physics, vol. 44, 341-356 (2003).
 A. Migdall, Correlated-Photon Metrology Without Absolute Standards, Physics Today 52, 41 (1999).
 A. V. Sergienko Quantum Metrology With Entangled Photons, in CXLVI International School of Physics [='Enrico Fermi'=], (T. J. Quinn, S. Leschiutta, and P. Tavella, editors), IOS Press, Amsterdam (ISBN 1 58603 167 8) ,715-746 (2001).