Precision Measurement
Research Projects
PMG has three key strands of activities that we have divided to make the program more digestible – however, it is worth understanding that all of us are working together in almost every stream since there is a high degree of overlap across the three strands.
STREAM A: CLOCKS AND TIME
This stream concerns the construction of the next generation of clocks, oscillators and lasers together with research into high-fidelity techniques for distributing their output signals over optical fibre networks.
Compact Clocks and Sensors (with U. Limoges, UQ): Three of our projects are aimed at developing compact and portable clocks that can deliver laboratory performance in the field: (i) trapping vapours within the hollow-core of a photonic-crystal optical fibre and then interrogating this vapour using Doppler-free techniques; (ii) locking lasers to special optical modes trapped within highly-polished millimetre-scale crystalline resonators. We believe that these devices could be very sensitive detectors of particular biological substances since their surface can be sensitized to target the desired substance; and (iii) compact atomic-beam standards with special interrogation techniques to reject unwanted effects arising from fast motion of the atoms. This offers the potential for a clock with state of the art performance but within a portable device.
Microwave Oscillators: A long-standing research project for us is the development of cryogenic microwave oscillators with superb frequency stability and phase fluctuations that can be a million times smaller than the best quartz oscillators. We see a major application for this technology as the master oscillator for micro-Doppler radar systems as well as millimeter-wave VLBI radio-astronomy observations. These cryogenic clocks devices already exhibit world-leading performance characteristics for any clock or oscillator and find use in some of the world’s best metrological laboratories.
Millihertz Lasers (with Humboldt University and PTB, Germany): The limit to the ultimate linewidth of a laser is set by fundamental length fluctuations in the materials that make up their frequency reference cavity (related to Brownian motion). We are currently developing a laser that uses a reference cavity that has been cooled to 3K inside a closed-cycle cryo-cooler. We predict that we should be able to achieve a linewidth of just 10s of millihertz: given that the laser frequency itself is 200 trillion Hertz one can gain an understanding of the incredible precision of these systems.
Time and Frequency Dissemination (together with UWA, NMI, MQU, ANU et al): The group has developed technology for distributing radio, microwave, and optical frequency signals over standard installed optical fibre networks for the purposes of synchronization or accurate timing. This technology actively measures and stabilises environmental fluctuations of the length of the fibre link, thereby allowing for transfers with a precision three orders-‐of-‐magnitude greater than satellite link technologies. Recent developments include the ability to transmit microwave frequencies with a precision that is normally only achieved using optical frequency transfer, as well as a technique for distribution to multiple independent nodes on a branching optical-‐fibre network. Both techniques are intrinsically narrowband and so can co-‐exist with digital data travelling on the same fibre. We have demonstrated this on fibre runs of up to 70km, and are currently extending this to many 100s of kilometres. This project can support distributed radar and radio-astronomy applications.
C. Perrella, P. S. Light, T. M. Stace, F. Benabid and A. N. Luiten, “High-resolution optical spectroscopy in a hollow-core photonic crystal fiber,” Phys. Rev. A 85 (2012) 012518
Fred N. Baynes, Michael E. Tobar, and Andre N. Luiten, “Oscillating Test of the Isotropic Shift of the Speed of Light”, Phys. Rev. Lett. 108, 260801 (2012), 10.1103/PhysRevLett.108.260801
J.G. Hartnett, N.R. Nand and C. Lu, Ultra-low-phase-noise cryocooled microwave dielectric-sapphire-resonator oscillators, Appl. Phys. Lett., 100, 183501, (2012)
N.R. Nand, J.G. Hartnett, E.N. Ivanov, G. Santarelli, Ultra-stable very-low-phase-noise signal source for Very Long Baseline Interferometry using a cryocooled sapphire oscillator, IEEE Trans on MTT, 59, 11, 2978 - 2986, (2011).
J.G. Hartnett and A.N. Luiten, Colloquium: Comparison of astrophysical and terrestrial frequency standards, Rev. Mod. Phys., 83, 1-9, (2011)
McFerran, John J. ; Hartnett, John Gideon ; Luiten, André N , An optical beam frequency reference with 10-14 range frequency instability, Applied Physics Letters, v95, (2009) DOI: 10.1063/1.3184578, pp. 031103 - 031103-3
STREAM B: FREQUENCY COMBS AND SPECTROSCOPY
Laser Absorption Spectroscopy (with UQ and UWA): We are developing ultra-high resolution atomic spectroscopy for the purposes of redefining the fundamental unit of temperature, the Boltzmann constant. This has required the development of techniques that have pushed spectroscopic accuracy to the limits imposed by quantum mechanics. We have used similar laser absorption techniques to develop a highly-sensitive atomic magnetometers for applications in bio-magnetic field detection.
Frequency Comb Spectroscopy (with UQ and UWA): Despite our successes with conventional spectroscopic techniques, we see a potential paradigm shift in spectroscopy based on the use of the 2005 Nobel Prize invention called a “frequency comb”. Frequency combs generate millions of discrete laser signals across large swathes of the optical spectrum; however, every one of these laser signals has a precisely known frequency.
We were the originators of this field in Australia and have developed techniques to manipulate these frequency combs so that they can be optimized for various objectives. The breakthrough application for the frequency comb (pioneered by workers at NIST/JILA in the USA) is to use them in a new type of massively parallel spectroscopy: one can instantaneously sample millions of spectroscopic points of some substance of interest.
This approach maximizes the information that can be extracted in an available measurement time and delivers excellent selectivity and sensitivity because of the broad range of spectral sampling. This is particularly the case when trying to understand complex molecular spectra in the presence of contaminating substances. We see some powerful applications in medical diagnosis by low-level components in the exhaled breath as well as detection of contamination and pollution in various industrial applications.
Gar-Wing Truong, Eric F. May, Thomas M. Stace and Andre Luiten, "Quantitative atomic spectroscopy for primary thermometry", Physical Review A 83, 033805 (2011).
Truong, GW, Anstie, JD May, EF; Stace, TM , Luiten, AN, “Absolute absorption line-shape measurements at the shot-noise limit”, Physical Review A 86 (3), 030501 ( 2012).
Thomas M. Stace, Gar-Wing Truong, James Anstie, Eric F. May, and André N. Luiten, “Power-dependent line-shape corrections for quantitative spectroscopy”, Phys. Rev. A 86, 012506 (2012)
STREAM C: QUANTUM FIBRE PHOTONICS
Over the last 5 years we have been exploiting the potential for photonic-crystal hollow-core optical fibre to provide an ideal communication path between the external macroscopic world and atoms that are trapped in the hollow‐core of the fibre. The small dimensions and guiding properties of the fibre lead to very strong coupling between the guided optical mode of the fibre and the internal states of the atoms.
Hand-held Optical Clocks (with U. Limoges): we have constructed optical clocks based on trapping iodine vapour or Rubidium vapour within the hollow core of the fibre. The performance of both of these devices is already comparable to the best quartz oscillators although we believe that this could potentially be improved by several orders of magnitude to be comparable to the best commercial clocks. The beauty of the fibre solution is that an eventual engineered standard could be matchbox-‐sized with a weight of a few hundred grams
Deterministic Optical Quantum Computing (with UQ, U.Limoges): The small dimensions of the fibre, and its arbitrary length, mean that we can create exceedingly strong interactions between light beams of different wavelength that are travelling through the same fibre (mediated by the atomic vapour). This type of light‐by-light interaction is the critical missing‐piece in deterministic optical quantum computing. Our preliminary demonstrated interactions are still thousands of times too weak to make the desired breakthrough – however, we have good reason to suppose that with additional effort these results could be improved substantially.
Cold Atom Guidance: The group is currently undertaking experiments to load laser-cooled atoms into hollow-core fibre and to guide and trap them within the fibre. This approach has the potential to deliver cold atoms to a desired location and also allow cold atom experiments outside the vacuum system.
P. S. LIGHT, F. Couny, Y. Y. Wang, N. V. Wheeler, P. J. Roberts and F. Benabid, “Double photonic bandgap hollow-core photonic crystal fiber,” Opt. Express 17 (2009) 16238-16243
J. Poulin, P. S. LIGHT, R. Kashyap and A. N. Luiten, “Optimized coupling of cold atoms into a fiber using a blue-detuned hollow-beam funnel,” Phys. Rev. A 84 (2011) 053812
C. Perrella, P. S. Light, J. D. Anstie, T. M. Stace, F. Benabid, and A. N. Luiten, High-resolution two-photon spectroscopy of rubidium within a confined geometry, PHYSICAL REVIEW A 87, 013818 (2013)
C. Perrella, P. S. Light, J. D. Anstie, F. Benabid, T. M. Stace, A. G. White, and A. N. Luiten, High Efficiency Cross-Phase Modulation in a Gas-filled Waveguide, in review,
Lurie, Anna; Baynes, Fred N; Anstie, James D; Light, Philip S; Benabid, Fetah; Stace, Thomas M; Luiten, Andre N, “High-performance iodine fiber frequency standard”, Vol. 36 Issue 24, pp.4776-4778 (2011)
