Fully reconfigurable coherent optical vector–matrix multiplication

Optics Letters The Optical Society 45 (2020) 5752-5752

J Spall, X Guo, TD Barrett, A Lvovsky

Optics is a promising platform in which to help realise the next generation of fast, parallel and energy-efficient computation. We demonstrate a reconfigurable free-space optical multiplier that is capable of over 3000 computations in parallel, using spatial light modulators with a pixel resolution of only 340x340. This enables vector-matrix multiplication and parallel vector-vector multiplication with vector size of up to 56. Our design is the first to simultaneously support optical implementation of reconfigurable, large-size and real-valued linear algebraic operations. Such an optical multiplier can serve as a building block of special-purpose optical processors such as optical neural networks and optical Ising machines.

Exploratory combinatorial optimization with reinforcement learning

Proceedings of the AAAI Conference on Artificial Intelligence Association for the Advancement of Artificial Intelligence 34 (2020)

T Barrett, WR Clements, JN Foerster, AI Lvovsky

Many real-world problems can be reduced to combinatorial optimization on a graph, where the subset or ordering of vertices that maximize some objective function must be found. With such tasks often NP-hard and analytically intractable, reinforcement learning (RL) has shown promise as a framework with which efficient heuristic methods to tackle these problems can be learned. Previous works construct the solution subset incrementally, adding one element at a time, however, the irreversible nature of this approach prevents the agent from revising its earlier decisions, which may be necessary given the complexity of the optimization task. We instead propose that the agent should seek to continuously improve the solution by learning to explore at test time. Our approach of exploratory combinatorial optimization (ECO-DQN) is, in principle, applicable to any combinatorial problem that can be defined on a graph. Experimentally, we show our method to produce state-of-the-art RL performance on the Maximum Cut problem. Moreover, because ECO-DQN can start from any arbitrary configuration, it can be combined with other search methods to further improve performance, which we demonstrate using a simple random search.

Roadmap on STIRAP applications

Journal of Physics B: Atomic, Molecular and Optical Physics IOP Publishing 52 (2019) 202001

K Bergmann, HC Naegerl, C Panda, A Kuhn

STIRAP (stimulated Raman adiabatic passage) is a powerful laser-based method, usually involving two photons, for efficient and selective transfer of populations between quantum states. A particularly interesting feature is the fact that the coupling between the initial and the final quantum states is via an intermediate state, even though the lifetime of the latter can be much shorter than the interaction time with the laser radiation. Nevertheless, spontaneous emission from the intermediate state is prevented by quantum interference. Maintaining the coherence between the initial and final state throughout the transfer process is crucial. STIRAP was initially developed with applications in chemical dynamics in mind. That is why the original paper of 1990 was published in The Journal of Chemical Physics. However, from about the year 2000, the unique capabilities of STIRAP and its robustness with respect to small variations in some experimental parameters stimulated many researchers to apply the scheme to a variety of other fields of physics. The successes of these efforts are documented in this collection of articles. In Part A the experimental success of STIRAP in manipulating or controlling molecules, photons, ions or even quantum systems in a solid-state environment is documented. After a brief introduction to the basic physics of STIRAP, the central role of the method in the formation of ultracold molecules is discussed, followed by a presentation of how precision experiments (measurement of the upper limit of the electric dipole moment of the electron or detecting the consequences of parity violation in chiral molecules) or chemical dynamics studies at ultralow temperatures benefit from STIRAP. Next comes the STIRAP-based control of photons in cavities followed by a group of three contributions which highlight the potential of the STIRAP concept in classical physics by presenting data on the transfer of waves (photonic, magnonic and phononic) between respective waveguides. The works on ions or ion strings discuss options for applications, e.g. in quantum information. Finally, the success of STIRAP in the controlled manipulation of quantum states in solid-state systems, which are usually hostile towards coherent processes, is presented, dealing with data storage in rare-earth ion doped crystals and in nitrogen vacancy (NV) centers or even in superconducting quantum circuits. The works on ions and those involving solid-state systems emphasize the relevance of the results for quantum information protocols. Part B deals with theoretical work, including further concepts relevant to quantum information or invoking STIRAP for the manipulation of matter waves. The subsequent articles discuss the experiments underway to demonstrate the potential of STIRAP for populating otherwise inaccessible high-lying Rydberg states of molecules, or controlling and cooling the translational motion of particles in a molecular beam or the polarization of angular-momentum states. The series of articles concludes with a more speculative application of STIRAP in nuclear physics, which, if suitable radiation fields become available, could lead to spectacular results.

Birefringent cavities: Effects and applications of a new paradigm in CQED

2019 Conference on Lasers and Electro-Optics Europe and European Quantum Electronics Conference, CLEO/Europe-EQEC 2019 (2019)

TD Barrett, TH Doherty, B Yuen, A Kuhn

© 2019 IEEE. The enhanced interaction of quantum states of light and matter within an optical resonator is a powerful tool for both addressing fundamental questions of nature and pursuing quantum technologies. Here, we discuss the impact of cavity birefringence - a lifting of the degeneracy of polarisation modes within the resonator - on both of these challenges. A novel model for such systems is experimentally verified by the cavity emission of single photons with time-dependent polarisation states that evolve along their wavepacket [1]. This model is then used to demonstrate how a tailored birefringence allows for enhanced photon emission beyond previous limitations [2].

Multimode interferometry for entangling atoms in quantum networks

Quantum Science and Technology IOP Publishing (2019)

TD Barrett, A Rubenok, D Stuart, O Barter, A Holleczek, J Dilley, P Nisbet-Jones, K Poulios, G Marshall, J O'Brien, A Politi, J Matthews, A Kuhn

Polarisation Oscillations in Birefringent Emitter-Cavity Systems

Physical Review Letters American Physical Society (2019)

TD Barrett, O Barter, D Stuart, B Yuen, A Kuhn

We present the effects of resonator birefringence on the cavity-enhanced interfacing of quantum states of light and matter, including the first observation of single photons with a time-dependent polarisation state that evolves within their coherence time. A theoretical model is introduced and experimentally verified by the modified polarisation of temporally-long single photons emitted from a $^{87}$Rb atom coupled to a high-finesse optical cavity by a vacuum-stimulated Raman adiabatic passage (V-STIRAP) process. Further theoretical investigation shows how a change in cavity birefringence can both impact the atom-cavity coupling and engender starkly different polarisation behaviour in the emitted photons. With polarisation a key resource for encoding quantum states of light and modern micron-scale cavities particularly prone to birefringence, the consideration of these effects is vital to the faithful realisation of efficient and coherent emitter-photon interfaces for distributed quantum networking and communications.

Benchmarking modern algorithms to holographically create optical tweezers for laser-cooled atoms

JOURNAL OF MODERN OPTICS 65 (2018) 2133-2141

N Holland, D Stuart, O Barter, A Kuhn

Nonlinear Zeeman effects in the cavity-enhanced emission of polarised photons


TD Barrett, D Stuart, O Barter, A Kuhn

Single-atom trapping and transport in DMD-controlled optical tweezers


D Stuart, A Kuhn

Interference of two pulse-like spatial beams with arbitrary transverse separation

Journal of Optics IOP Publishing 18 (2016) 125201-125201

J Flórez, J-R Álvarez, O Calderón-Losada, LJ Salazar-Serrano, A Valencia

Quantum Logic with Cavity Photons From Single Atoms


A Holleczek, O Barter, A Rubenok, J Dilley, PBR Nisbet-Jones, G Langfahl-Klabes, GD Marshall, C Sparrow, JL O'Brien, K Poulios, A Kuhn, JCF Matthews

Cavity Induced Interfacing of Atoms and Light

in Engineering the Atom-Photon Interaction: Controlling Fundamental Processes with Photons, Atoms and Solids, Springer (2015) 1
Part of a series from Nano Optics and Nano Photonics

A Kuhn

This chapter introduces cavity-based light-matter quantum interfaces, with a single atom or ion in strong coupling to a high-finesse optical cavity. We discuss the deterministic generation of indistinguishable single photons from these systems; the atom-photon entanglement intractably linked to this process; and the information encoding using spatio-temporal modes within these photons. Furthermore, we show how to establish a time-reversal of the aforementioned emission process to use a coupled atom-cavity system as a quantum memory. Along the line, we also discuss the performance and characterisation of cavity photons in elementary linear-optics arrangements with single beam splitters for quantum-homodyne measurements.

Qubits, qutrits, and ququads stored in single photons from an atom-cavity system


A Holleczek, O Barter, G Langfahl-Klabes, A Kuhn

Light interference In position and momentum variables: The spatial Alford and Gold effect

Proceedings of Frontiers in Optics 2015, FIO 2015 (2015)

J Flórez, O Calderó-Losada, LJ Salazar-Serrano, JR Álvarez-Velásquez, A Valencia

© 2015 Optical Society of America. Intensity modulation of two parallel-propagating beams is observed in the Fourier plane when the beams' separation is such that they do not interfere in position. This is analogous to the temporal Alford and Gold effect.

Cavity Induced Interfacing of Atoms and Light

Springer International Publishing (2015) 3-38

A Kuhn

Single Emitters in Isolated Quantum Systems

in Single-Photon Generation and Detection, Elsevier 45 (2013) 467-539
Part of a series from Experimental Methods in the Physical Sciences

GS Solomon, C Santori, A Kuhn

Photonic qubits, qutrits and ququads accurately prepared and delivered on demand


PBR Nisbet-Jones, J Dilley, A Holleczek, O Barter, A Kuhn

Control and manipulation of cold atoms in optical tweezers


C Muldoon, L Brandt, J Dong, D Stuart, E Brainis, M Himsworth, A Kuhn

Single-photon absorption in coupled atom-cavity systems

PHYSICAL REVIEW A 85 (2012) ARTN 023834

J Dilley, P Nisbet-Jones, BW Shore, A Kuhn

Highly efficient source for indistinguishable single photons of controlled shape


PBR Nisbet-Jones, J Dilley, D Ljunggren, A Kuhn