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2015 Research Highlights

 

Sensing Earth Rotation with a Helium-Neon Ring Laser Operating at 1.15 um

Sensing Earth Rotation with a Helium-Neon Ring Laser Operating at 1.15 um
The PR-1 Ring Laser Gyroscope

Ulrich Schreiber, K., Robert J. Thirkettle, Robert B. Hurst, David Follman, Garrett D. Cole, Markus Aspelmeyer, and Jon-Paul R. Wells. 2015. Optics Letters 40 (8): 1705. Doi:10.1364/OL.40.001705.

This paper reports on the operation of a 2.56 m2 helium-neon based ring laser interferometer at a wavelength of 1.152276 micron using GaAs based crystalline coated intra-cavity supermirrors. This work represents the first implementation of crystalline coatings in an active laser system and expands the core application area of these low-thermal-noise cavity end mirrors to inertial sensing systems.

For the first time at this wavelength, the ring laser is observed to unlock on the bias provided by Earth rotation alone, yielding a Sagnac frequency of approximately 59 Hz. Owing to the fact that the laser is situated in the Rutherford building of the Ilam campus of the University of Canterbury, the power spectrum derived from the Sagnac time series exhibits both an Earth line and sidebands at 2.36 Hz due to the rocking motion of the building.

This ring gyroscope, together with similar apparatus in Germany provides a unique high-precision tool for geophysical observation.

 

Temporal tweezing of light

Temporal tweezing of light

Jae K. Jang, Miro Erkintalo, Stéphane Coen, and Stuart G. Murdoch, Nature Commun. 6, 7370 (2015)

doi:10.1038/ncomms8370

Catch a pulse of light, and nudge it a bit; forward or backward. Conventional optical tweezers manipulate physical objects in space using laser light. Here we report on the similar manipulation of light itself, but in time: the temporal tweezing of light. We selectively move around in time ultrashort light pulses with respect to, and independently of each other. Never before has such exquisite control over light been achieved.

The pulses we manipulate are temporal cavity solitons (CSs): packets of light persisting in an optical fiber loop. Multiple solitons can be independently present at arbitrary temporal positions around the cavity, encoding binary data. As solitons, these pulses do not disperse over time. Their power losses are also balanced by an external continuous-wave laser beam coherently driving the cavity. This ensures propagation and storage of CSs for unlimited time. Manipulation of these solitons immediately enables all-optical reconfiguration of a binary data stream, with potential benefits for optical information processing.

 

 

Identifying a superfluid Reynolds number via dynamical similarity

Identifying a superfluid Reynolds number via dynamical similarity

Reeves, M. T., T. P. Billam, B. P. Anderson, and A. S. Bradley. 2015. Physical Review Letters 114 (15). Doi:10.1103/PhysRevLett.114.155302. [Editor’s suggestion].

The Reynolds number provides a characterization of the transition to turbulent flow, with wide application in classical fluid dynamics. Identifying such a parameter in superfluid systems is challenging due to their fundamentally inviscid nature, yet superfluids exhibit emergent effective viscosity arising from the nucleation of quantum vortices. A perceptive observation was made in 1953 when Onsager noted that the circulation of a single quantum vortex has the same dimension as the classical kinematic viscosity.

Performing the first systematic study of superfluid cylinder wakes in two dimensions, we observe dynamical similarity of the frequency of vortex shedding by a cylindrical obstacle. An example of the vortex field shed in the obstacle wake is shown in Figure 1. The universality of the turbulent wake dynamics is revealed by expressing shedding frequencies in terms of an appropriately defined superfluid Reynolds number, Res, that accounts for the breakdown of superfluid flow through quantum vortex shedding. For large obstacles, the dimensionless shedding frequency exhibits a universal form that is well-fitted by a classical empirical relation. The form of Res suggests it may also have universal applicability beyond 2D. Indeed, Res has already been used to successfully analyse the transition to 3D quantum turbulence in superfluid helium experiments.

 

Optically addressable nuclear spins in a solid with a six-hour coherence time

Optically addressable nuclear spins in a solid with a six-hour coherence time
Photo: Otago Daily Times

Zhong, Manjin, Morgan P. Hedges, Rose L. Ahlefeldt, John G. Bartholomew, Sarah E. Beavan, Sven M. Wittig, Jevon J. Longdell, and Matthew J. Sellars. 2015. Nature 517 (7533): 177–80. Doi:10.1038/nature14025.

This collaborative work demonstrates coherent storage of optical information in nuclear spins for record breaking periods of time. The experiments were actually performed at the ANU in Canberra in the lab of Matt Sellars, but a similar system exists in Longdell’s lab at the DWC in Otago (as illustrated on the cover of this Annual Report). Long term quantum storage of light is necessary for many of the uses of quantum information, most immediately in extending the reach of quantum networks. This work shows a coherence decay well within the timescale needed for global optical communication. In fact the coherence times are so long that a device containing these nuclear spins traveling at just 9 km per hour would have lower decoherence with distance than light in an optical fibre.

This is noteworthy because prior to this work it had been almost universally assumed that light is the best long-distance carrier of quantum information. Perhaps future quantum key distribution for quantum cryptography might be via a “quantum USB stick”.

 

 

Breakdown of Photon Blockade: A Dissipative Quantum Phase Transition in Zero Dimensions

Breakdown of Photon Blockade: A Dissipative Quantum Phase Transition in Zero Dimensions

H. J. Carmichael, Phys. Rev. X, 5, 031028 (2015) doi:10.1103/PhysRevX.5.031028

The Jaynes Cummings model is one of the most important in quantum optics. It describes a single quantised radiation mode of a resonator strongly interacting with two level systems. The model was initially developed to describe the situations where these two level systems were atoms, however it also describes the situations where the two level systems are superconducting qubits. The use of superconducting qubits (“circuit QED”) has allowed new parameter regimes of the Jaynes-Cummings model to be reach experimentally and raised new interest in the basic physics of the Jaynes-Cummings model.

An important behaviour that is implemented by the Jaynes-Cummings model is the “photon-blockade”. The most basic example of this is where a single photon in the resonator has the effect of detuning the resonator far enough that subsequent photons cannot enter. Photon blockades exist at higher photon numbers also. The photon blockade is not, however, an absolute barrier to the absorption of additional photons, and this work investigates how the breakdown of photon blockages occurs. Blockade arises as an excitation bottleneck caused by detuning when one tries to drive monochromatic photons up an energy ladder of unequal steps. In principle, it can be broken through, since increasing drive strength both shifts and broadens energy levels, increasing the probability for multiphoton absorption up many steps of the ladder. This paper shows that the breaking through—the breakdown of photon blockade—is organized around a dissipative quantum phase transition.