CQT - Colloquia

CQT Colloquium by Aephraim Steinberg, University of Toronto

Title: Everything you always wanted to know about atom tunneling & photon propagation but were afraid to ask
Date/Time: 20-Feb, 04:00PM
Venue: CQT Level 3 Seminar room, S15-03-15

If there are two problems you would think quantum mechanicists & opticians had beaten to death, they might be quantum tunneling and the propagation of photons through a cloud of atoms.

And yet when you look more deeply – and ask “where are the atoms while they’re tunneling through the forbidden region, and how much time do they spend there?”or “how do photons get slowed down, and where is the energy spending its time?”– the answers are not so simple.

I will describe two experiments looking into aspects of “quantum retrodiction.” In the first, we measure how long Bose-condensed atoms spend inside a potential barrier (created by a far-detuned laser beam focused to 1 micron)before being transmitted; I will also talk about some predictions regarding what insidious effects actually observing a particle in the barrier could have. In the second, we measure the amount of time atoms spend in the excited state when a resonant photon is not absorbed by those atoms, but propagates clear through. We find, surprisingly, that the answer need not even be a positive number. I will connect this to better-known aspects of optical propagation.

Time permitting, I will also say a few words about the observation of (initially)surprising “spin textures” in the tunneling cloud that illuminate novel features of cold-atom magnetohydrodynamics; and planned experiments to study the timescales relevant to quantum measurement in a tunneling scenario.

REFERENCES:

[1]Measuring the time a tunnelling atom spends in the barrier, Ramón Ramos, David Spierings, Isabelle Racicot, & Aephraim M. Steinberg, Nature 583, 529(2020).

[2]Observation of the decrease of Larmor tunneling times with lower incident energy, David C. Spierings, & Aephraim M. Steinberg, Phys. Rev. Lett. 127,133001 (2021).

[3]Spin Rotations in a Bose-Einstein Condensate Driven by Counterflow and Spin-independent Interactions, David C. Spierings, Joseph H. Thywissen, & Aephraim M. Steinberg, Phys. Rev. Lett. 132, 173401 (2024).

[4]Measuring the time atoms spend in the excited state due to a photon they do not absorb, Josiah Sinclair, Daniela Angulo, Kyle Thompson, Kent Bonsma-Fisher,Aharon Brodutch, & Aephraim M. Steinberg, PRX Quantum 3, 010314 (2022).

[5]How much time does a resonant photon spend as an atomic excitation before being transmitted?, Kyle Thompson, Kehui Li, Daniela Angulo, Vida-Michelle Nixon,Josiah Sinclair, Amal Vijayalekshmi Sivakumar, Howard M. Wiseman, & Aephraim M. Steinberg, quant-ph/2310.00432 (2023)

[6]Experimental evidence that a photon can spend a negative amount of time in anatom cloud, Daniela Angulo, Kyle Thompson, Vida-Michelle Nixon, Andy Jiao ,Howard M. Wiseman, & Aephraim M. Steinberg, quant-ph/2409.03680 (2024)

CQT Colloquium by Simon Cornish, Durham University

Title: Dipolar interactions between ultracold RbCs molecules in magic traps and optical tweezers
Date/Time: 26-Sep, 04:00PM
Venue: CQT Level 3 Seminar Room, S15-03-15

Ultracold polar molecules are an exciting platform for quantum science and technology. The combination of rich internal structure of vibration and rotation, controllable long-range dipolar interactions and strong coupling to applied electric and microwave fields has inspired many applications. These include quantum simulation of strongly interacting many-body systems, the study of quantum magnetism, quantum metrology and molecular clocks, quantum computation, precision tests of fundamental physics and the exploration of ultracold chemistry. Many of these applications require full quantum control of both the internal and motional degrees of freedom of the molecule at the single particle level.In Durham, we study ultracold ground-state RbCs molecules formed by associating Rb and Cs atoms using a combination of magnetoassociation and stimulated Raman adiabatic passage [1]. This talk will report our work on the development of full quantum control of the molecules. Specifically, I will explain how we have mastered the ac Stark shift due to the trapping light [2] to demonstrate robust storage qubits in the molecule [3] and will describe the development of magic traps [4] that support second-scale rotational coherences giving access to controllable dipolar interactions [5]. I will also report on new experiments that produce single molecules in optical tweezers starting from a single Rb and a single Cs atom [6]. Using this platform, we prepare the molecules in the motional ground state of the trap and can perform addressing and detection of single molecules [7]. Using mid-sequence detection of formation errors, we demonstrate rearrangement to produce small defect-free arrays [8]. By transferring the molecules into magic-wavelength tweezers, we can prepare long-lived rotational coherences that support spin-exchange interactions between molecules, enabling the preparation of maximally entangled entangled Bell states with high fidelity.Finally, as an outlook, we demonstrate a new hybrid platform that combines single ultracold molecules with single Rydberg atoms [9], opening up the prospect of non-destructive readout of the molecular state and fast entangling gates. [1] P.K.Molony et al., “Creation of Ultracold RbCs Molecules in the Rovibrational Ground State”, Phys. Rev. Lett. 113, 255301 (2014).[2] P.D.Gregory et al., “ac Stark effect in ultracold polar RbCs molecules”, Phys. Rev. A 96, 021402(R) (2017).[3] P.D.Gregory et al., “Robust storage qubits in ultracold polar molecules”, Nature Physics 17, 1149-1153 (2021).[4] Q.Guan et al., “Magic conditions for multiple rotational states of bialkali molecules in optical lattices”, Phys. Rev. A 103, 043311 (2021).[5] P.D.Gregory et al., “Second-scale rotational coherence and dipolar interactions in a gas of ultracold polar Molecules”, Nature Physics 20, 415—421 (2024).[6] R.V.Brooks et al., “Preparation of one Rb and one Cs atom in a single optical tweezer”, New J. Physics 23, 065002 (2021).[7] D.K.Ruttley, A.Guttridge et al., “Formation of ultracold molecules by merging optical tweezers”,Phys. Rev. Lett. 130, 223401 (2023).[8] D.K.Ruttley et al., “Enhanced Quantum Control of Individual Molecules Using Optical Tweezer Arrays”, PRX Quantum 5, 020333 (2024).[9] A.Guttridge, D.K.Ruttley et al., “Observation of Rydberg blockade due to the charge-dipole interaction between an atom and a polar molecule”, Phys. Rev. Lett. 131, 013401 (2023).

CQT Colloquium by Edward Yu, University of Texas

Title: Semiconductor Physics and Devices across Length Scales for Quantum and Energy Applications
Date/Time: 03-Sep, 12:00PM
Venue: CQT Level 3 Seminar room, S15-03-15

Title: Semiconductor Physics and Devices across Length Scales for Quantum and Energy ApplicationsAbstract: Semiconductor materials are foundational to technologies ranging from computing to communications to renewable energy. In nearly all cases, control over structure and electronic properties at or near the nanometer scale is essential. However, the dimensions over which such control must be exercised can vary dramatically — from nanometers to meters or larger. We will discuss a variety of recent projects in our laboratory in which semiconductor material and device properties must be controlled or characterized at or near nanometer length scales, but for which the relevant scale for useful application ranges from microns to meters or larger. First, we discuss studies of monolayer transition metal dichalcogenide semiconductors, in which single photon emission can be observed in the presence of tensile strain. We show how proximal probe measurements with a back-gated sample geometry allow the full strain tensor of monolayer transition metal dichalcogenide semiconductors to be measured with spatial resolution of tens of nanometers [1]. These studies provide insight into actual nanoscale strain configurations in geometries for which single photon emission is typically observed, and also enable characterization of phenomena such as piezoelectricity at the nanoscale. We then discuss studies in which strain can be controlled dynamically via electrostatically induced deflection of monolayer WSe2 membranes, an approach with the potential to enable electrical control over single photon emission. In the second part of the presentation, we discuss a variety of approaches for exploiting concepts and processes from the realm of semiconductor manufacturing and device physics — band structure engineering, resistive switching, and nanoscale thin-film reactions — to fabricate photoelectrodes for solar-powered splitting of water molecules into hydrogen and oxygen [2-4]. Our recent results in this area suggest an approach for creation of photoelectrodes for green hydrogen production with scalability and costs similar to those for silicon photovoltaics, thereby offering intriguing prospects for cost-effective green hydrogen production [5]. Time permitting, we will also discuss how control over and understanding of strain at the nanoscale provides a link between these seemingly disparate applications.[1] Nano Lett. 24, 1835-1842 (2024).[2] Nature Nanotechnol. 10, 84-90 (2015).[3] Nature Mater. 16, 127-131 (2017).[4] Nature Commun. 12, 3982 (2021).[5] ACS Appl. Energy Mater. 7, 3253-3262 (2024).

CQT Colloquium by Michael Tobar, University of Western Australia

Title: Precision Metrology with Photons, Phonons and Spins: Answering Major Unsolved Problems in Physics and Advancing Translational Science
Date/Time: 14-Jul, 03:00PM
Venue: CQT Level 3 Seminar Room, S15-03-15

Abstract: The Quantum Technologies and Dark Matter research laboratory has a rich history of developing precision tools for both fundamental physics and industrial applications. This includes the development and application of novel low-loss and highly sensitive resonant photonic and phononic cavities, such as whispering gallery and re-entrant cavities, as well as photonic band gap and bulk acoustic wave structures. These cavities have been used in a range of applications, including highly stable low noise classical and atomic oscillators, low noise measurement systems, highly sensitivity displacement sensors, high precision electron spin resonance and spin-wave spectroscopy, high precision measurement of material properties and applications of low-loss quantum hybrid systems, which are strongly coupled to form polaritons or quasi-particles. Translational applications of our technology has included the realization of the lowest noise oscillators and systems for advance radar, the enabling of high accuracy atomic clocks and ultra-sensitive transducers for precision gravity measurements.

Meanwhile, there is currently a world-wide renascence to adapt precision and quantum measurement techniques to major unsolved problems in physics. This includes the effort to discover “Beyond Standard Model” physics, including the nature of Dark Matter, Dark Energy and the unification of Quantum Mechanics with General Relativity to discover the unified theory of everything. Thus, the aforementioned technology has been adapted to realize precision measurement tools and techniques to test some of these core aspects of fundamental physics, such as searches for Lorentz invariance violations in the photon, phonon and gravity sectors, possible variations in fundamental constants, searches for wave-like dark matter and test of quantum gravity. This work includes: 1) Our study and application of putative modified physical equations due to beyond standard model physics, to determine possible new experiments: 2) An overview of our current experimental program, including status and future directions. This includes experiments that take advantage of axion-photon coupling and axion-spin coupling to search for axion dark matter. High acoustic Q phonon systems to search for Lorentz violations, high frequency gravity waves, scalar dark matter and tests of quantum gravity from the possible modification of the Heisenberg uncertainty principle.

CQT Colloquium by Ron Folman, Ben-Gurion University of the Negev

Title: Matter-wave interferometers on the atom chip
Date/Time: 28-Oct, 04:00PM
Venue: Online via Zoom

Abstract: Matter-wave interferometry provides an excellent tool for fundamental studies as well as technological applications. In our group, several interferometry experiments have been done with a BEC on an atom chip [1] examining different effects. For example, we studied fluctuations in the nearby environment by an interference of atoms trapped in a magnetic lattice very close (5μm) to a room temperature surface [2,3]. We realized a new interferometry scheme of self-interfering clocks and showed, in a proof-of-principle experiment, how this could probe the interplay of QM and GR [4]. We also described a rule for “clock complementarity”, which we deduce theoretically and verify experimentally [5]. In the clock interferometer, we have observed phase jumps due to the existence of a geometric phase [6]. Furthermore, we realized Stern-Gerlach interferometry [7-10] despite several theoretical works which have shown over the years that fundamental barriers exist.

I will give a brief description of the advantages of the atom chip, and will then describe several of the interferometric schemes, and their connection to issues such as environmentally and gravitationally (red-shift) induced decoherence, as well as loss of coherence due to interferometer imprecision (the humpty-dumpty effect). I will conclude with an outlook concerning ideas for possible tests of exotic physics such as quantum gravity [11], and mention several speculations which we hope to examine in the future.

[1] M. Keil et al., “Fifteen years of cold matter on the atom chip: Promise, realizations and prospects”, Journal of Modern Optics 63, 1840 (2016).
[2] S. Zhou et al., “Robust spatial coherence 5µm from a room temperature atom-chip”, Phys. Rev. A 93, 063615 (2016).
[3] Y. Japha et al., “Suppression and enhancement of decoherence in an atomic Josephson junction”, New J. Phys. 18, 055008 (2016).
[4] Y. Margalit et al., “A self-interfering clock as a ‘which path’ witness”, Science 349, 1205 (2015).
[5] Z. Zhou et al., “Clock complementarity in the context of general relativity”, Classical and Quantum Gravity 35, 185003 (2018).
[6] Zhifan Zhou, Yair Margalit, Samuel Moukouri, Yigal Meir, and Ron Folman “An experimental test of the geodesic rule proposition for the non-cyclic geometric phase”, Science Advances 6, eaay8345 (2020).
[7] S. Machluf et al., “Coherent Stern-Gerlach momentum splitting on an atom chip”, Nature Communications 4, 2424 (2013).
[8] Y. Margalit et al., “Analysis of a high-stability Stern-Gerlach spatial fringe interferometer”, New J. Phys. 21, 073040 (2019).
[9] O. Amit, Y. Margalit, O. Dobkowski, Z. Zhou, Y. Japha, M. Zimmermann, M. A. Efremov, F. A. Narducci, E. M. Rasel, W. P. Schleich, R. Folman. “T3 Stern-Gerlach matter-wave interferometer”, Phys. Rev. Lett. 123, 083601 (2019).
[10] Mark Keil, Shimon Machluf, Yair Margalit, Zhifan Zhou, Omer Amit, Or Dobkowski, Yonathan Japha, Samuel Moukouri, Daniel Rohrlich, Zina Binstock, Yaniv Bar-Haim, Menachem Givon, David Groswasser, Yigal Meir, Ron Folman, “Stern-Gerlach Interferometry with the Atom Chip”, Invited review paper, in a book in honor of Otto Stern (Springer), https://arxiv.org/abs/2009.08112 (2021).
[11] Yair Margalit, Or Dobkowski, Zhifan Zhou, Omer Amit, Yonathan Japha, Samuel Moukouri, Daniel Rohrlich, Anupam Mazumdar, Sougato Bose, Carsten Henkel, Ron Folman, “Realization of a complete Stern-Gerlach interferometer: Towards a test of quantum gravity”, Science advances 7, eabg2879 (2021).

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CQT Colloquium by Nobuyuki Imoto, Osaka University

Title: CQT Colloquium by Nobuyuki Imoto, Osaka University
Date/Time: 02-Nov, 04:00PM
Venue: CQT Level 3 Seminar Room, S15-03-15

Abstract: If a high-quality entanglement is shared between two distant parties, there are a lot of innovative things we can do such as device-independent QKD, which is in fact initiated by Ekert [1]. For this, faithful quantum communication via a noisy and lossy channel is an important element, which is the main research item of my research group [2]. As we proceed this type of research, we encounter some fundamental research themes. For example, we developed a frequency converter of a single photon that maintains coherence and entanglement [3]. Our frequency converter acts as a beamsplitter in frequency domain, whose conversion efficiency is tunable. Using this frequency-domain beamsplitter, we performed Hong-Ou-Mandel interference [4], where two different-color input photons are converted into two same-color output photons whose color stochastically becomes either of the original two colors. We also performed Mach-Zehnder interference [5], which, in frequency domain, is more difficult than the HOM interference. The second example of fundamental research themes, other than the frequency converter, is cheat-sensitive type communication [6], where we can guess the result of the measurement performed by our partner regardless whether he/she chose from the linear and circular polarization measurements, which at first glance appears to be in conflict with the uncertainty principle. The key is that we not only prepare the initial state of the photon before the partner’s measurement but also measure its final state after the partner’s measurement. This concept is generalized to so-called weak value [7], and we are pursuing the meaning and usage of this new concept [8]. [1] A. K. Ekert, PRL67, 661 (1991). [2] T. Yamamoto et al., Nature 421, 343-346 (2003); Nat. Photon. 2, 488 - 491 (2008). [3] R. Ikuta et al., Nat. Commun. 2, 1544 (2011). [4] T. Kobayashi et al., Nat. Photon. 10, 441—444 (2016). [5] T. Kobayashi et al., Optics Express, 25, 012052_1_9 (2017). [6] K. Shimizu et al., PRA84, 022308 (2011). [7] Y. Aharonov et al., PRL, 60, 1351 (1988). [8] K. Yokota et al., New J. Phys. 18, 123002 (2016).

CQT10 Colloquium by Dimitris Angelakis, CQT, NUS

Title: Quantum simulations with strongly interacting photons: Merging condensed matter with quantum optics for quantum technologies
Date/Time: 27-Jul, 04:00PM
Venue: CQT Seminar Room, S15-03-15

Abstract: Classical computers require enormous computing power and memory to simulate even the most modest quantum systems. That makes it difficult to model, for example, why certain materials are insulators and others are conductors or even superconductors. R. Feynman had grasped this since the 1980s and suggested to use instead another more controllable and perhaps artificial quantum system as a "quantum computer" or specifically in this case a "quantum simulator". Working examples of quantum simulators today include extremely cold atoms trapped with lasers and magnetic fields and ions in electromagnetic traps. Photons and polaritons in light-matter systems have also recently emerged as a promising avenue especially for simulating out of equilibrium many-body phenomena in a natural driven-dissipative setting. I will briefly review in non-specialist terms the main results in this area including the early ideas on realizing Mott insulators, Fractional Hall states and Luttinger liquids with photons [1,2,3]. After that I will present in more detail a recent experiment in many-body localization physics using interacting photons in the latest superconducting quantum chip of Google [4]. A simple method to study the energy-levels-and their statistics - of many-body quantum systems as they go through the ergodic to many-body localized (MBL) transition, was proposed and implemented. The formation of a mobility edge of an energy band was observed and its shrinkage with disorder toward the center of the bands was measured, a direct observation of a canonical condensed matter concept perhaps for the first time. Beyond the applications in understanding fundamental physics, the potential impact of this field in different areas of quantum and nano technology and material science will be touched upon. References 1. D.G. Angelakis and C. Noh “Many-body physics and quantum simulations with light” Report of Progress in Physics, 80 016401 (2016) 2. "Quantum Simulations with Photons and Polaritons: Merging Quantum Optics with Condensed Matter Physics" edited by D.G. Angelakis, Quantum Science and Technology Series, Springer International Publishing, 2017, ISBN 978-3-319-52023-0, DOI 10.1007/978-3-319-52025-4 3. Keil, Noh, Rai, Stutzer, Nolte, Angelakis, A. Szameit "Optical simulation of charge conservation violation and Majorana dynamics", Optica 2, 454 (2015) 4. P. Roushan, C. Neill, J. Tangpanitanon,V.M. Bastidas,, …, D.G. Angelakis, J. Martinis. “Spectral signatures of many-body localization of interacting photons”, under review

CQT Colloquium by Jukka Pekola, Aalto University

Title: Energy Fluctuations and Maxwell Demon in Nano-electronic Circuits
Date/Time: 25-Jul, 04:00PM
Venue: CQT Seminar Room, S15-03-15

Abstract: In small systems, such as molecules or nanostructures, energy fluctuations play an important role, and the second law of thermodynamics, for example, applies only on the average. The distribution of entropy production and the work performed under non-equilibrium conditions are then governed by so-called fluctuation relations [1 - 3]. I apply these concepts to a single-electron box [4,5], and present an experimental demonstration of fluctuation relations in them [6,7]. Single-electron circuits provide furthermore a basic example of a Maxwell Demon, where information can be converted into energy [8]; here the information is collected by a detector with single-electron sensitivity. Finally I discuss the subtle issues of work and heat in open quantum systems. I use superconducting qubits as examples of driven systems in this context [9,10]. [1] C. Jarzynski, Nonequilibrium equality for free energy differences, Phys. Rev. Lett. 78, 2690 (1997). [2] G. E. Crooks, Entropy production fluctuation theorem and the nonequilibrium work relation for free energy differences, Phys. Rev. E 60, 2721 (1999). [3] U. Seifert, Entropy Production along a Stochastic Trajectory and an Integral Fluctuation Theorem, Phys. Rev. Lett. 95, 040602 (2005). [4] D.V. Averin and J.P. Pekola, Statistics of the dissipated energy in driven single-electron transitions, EPL 96, 67004 (2011). [5] J. P. Pekola and O.-P. Saira, Work, Free Energy and Dissipation in Voltage Driven Single-Electron Transitions, J. Low Temp. Phys. 169, 70 (2012). [6] O.-P. Saira, Y. Yoon, T. Tanttu, M. Möttönen, D. V. Averin, and J. P. Pekola, Test of Jarzynski and Crooks fluctuation relations in an electronic system, Phys. Rev. Lett. 109, 180601 (2012). [7] J. V. Koski et al., Distribution of entropy production in nonequilibrium single-electron tunneling, arXiv:1303.6405. [8] D. V. Averin, M. Möttönen, and J. P. Pekola, Maxwell's demon based on a single-electron pump, Phys. Rev. B 84, 245448 (2011). [9] J. P. Pekola, P. Solinas, A. Shnirman, and D. V. Averin, Calorimetric measurement of quantum work, arXiv:1212.5808 (2012). [10] F. W. J. Hekking and J. P. Pekola, Quantum jump approach for work and dissipation in a two-level system, arXiv:1305.5207.

CQT Colloquium by Andrey Morello, ARC Centre of Excellence Centre for Quantum Computation and Communication Technology, The University of New South Wales

Title: Single-atom spin qubits in silicon
Date/Time: 25-Oct, 04:00PM
Venue: CQT Seminar Room, S15-03-15

Abstract: The idea of using the spin of a single donor atom in silicon to encode quantum information goes back to the Kane proposal [1] in 1998. The proposal was motivated by two observations: (i) Silicon is one of the most promising materials to host spin qubits in solid state, owing to the very weak spin-orbit coupling, and to the possibility to eliminate decoherence from nuclear spins by isotopic purification; (ii) A trillion-dollar worth industry already exists, that has developed extraordinary tools to manufacture silicon nanoscale devices in a reliable and cost-effective way. The proposal appeared ambitious, visionary but very challenging at the time, because it relied upon the non-trivial assumption that the progress in the fabrication of classical silicon devices could be harnessed to pursue quantum information goals. Indeed, over a decade of intense efforts has been necessary before the first breakthroughs in silicon quantum technologies could be demonstrated. I will present the first experimental demonstration of a qubit based on a single phosphorus atom in silicon. The atom is coupled to a silicon Single-Electron Transistor, and the whole device is fabricated retaining standard CMOS technologies such as ion implantation [2] and metal gates fabricated on top of high-quality silicon oxide [3]. In a single-atom device, we have demonstrated single-shot readout [4] and coherent control [5] of the donor electron spin, as well and the spins of the 31P nucleus and of a strongly-coupled 29Si nucleus. All three qubits exhibit excellent coherence and high-fidelity readability, with the nuclear ones being accessible through a quantum nondemolition measurement. These results represent major milestones in the search for a scalable and coherent quantum computer platform, and confirm the vision of silicon as the choice material for both quantum and classical technologies. [1] B. E. Kane, Nature 393, 133 (1998). [2] D. N. Jamieson et al., Appl. Phys. Lett. 86, 202101 (2005). [3] A. Morello et al., Phys. Rev. B 80, 081307(R) (2009). [4] A. Morello et al., Nature 467, 687 (2010). [5] J. J. Pla et al., Nature (2012), in press.

CQT Colloquium by Peter Hanggi, University of Augsburg

Title: Doing small systems: Fluctuation relations and the arrow of time
Date/Time: 26-Jul, 04:00PM
Venue: CQT Seminar Room, S15-03-15

Abstract: This talk is aimed at highlighting issues that relate of doing thermodynamics and statistical physics of finite size systems. This theme gained considerable importance in view of fascinating advances in nanotechnology and system biology. While the fathers of thermodynamics developed the famous 5 Laws of Thermodynamics (incl. a “—1_Law), having in mind macroscopic systems, these grand concepts need to be inspected anew in view of the fact that the fluctuations grow with decreasing size to a level where they even may play the dominant role. This holds true particularly for the inter-relationships between fluctuations and, importantly, the measurements of work, heat & heat flow and thermodynamic equilibrium quantifiers such as (non-fluctuating) free energy changes or production of thermodynamic entropy. -- Subtleties occur in equilibrium thermodynamics for small systems, such as the role of finite size for quantities like (possibly negative-valued) canonical heat capacitance in presence of strong system-environment coupling. I further elaborate on recent, timely results for nonequilibrium classical and quantum fluctuation relations. An attempt is made to outline pitfalls and still open issues (relativistic and others) together with those inherent difficulties that likely do emerge with the experimental validation scenarios of such relations. Finally, a connection between Fluctuation Relations, nonlinear Response and its feasible relation with the ever-lasting intriguing challenge in detecting the origin of an "Arrow of Time" will be elucidated. This presentation is based on joint work with Michele Campisi, Gert-Ludwig Ingold and Peter Talkner, all at the University of Augsburg. -- Own pertinent recent works that apply for the theme of this talk are: [1] G. L. Ingold, P. Hänggi, and P. Talkner Specific heat anomalies of open quantum systems Phys. Rev. E 79, 061105 (2009) [2] M. Campisi, P. Hanggi, and P. Talkner Colloquium: Quantum fluctuation relations: Foundations and applications Rev. Mod. Phys. 83, 771--791 (2011); Addendum and Erratum: Quantum fluctuation relations: Foundations and applications Rev. Mod. Phys. 83, 1653 (2011). [3] M. Campisi and P. Hanggi Fluctuation, Dissipation and the Arrow of Time Entropy 13, 2024--2035 (2012).

CQT Colloquium by Jeremy O'Brien, University of Bristol

Title: Integrated Quantum Photonics
Date/Time: 10-Feb, 04:00PM
Venue: CQT Seminar Room, S15-03-15

Abstract: Quantum information science aims to harness uniquely quantum mechanical properties to enhance measurement and information technologies, and to explore fundamental aspects of quantum physics. Of the various approaches to quantum computing [1], photons are particularly appealing for their low-noise properties and ease of manipulation at the single qubit level [2]. Encoding quantum information in photons is also an appealing approach to quantum communication, metrology (eg. [3]), measurement (eg. [4]) and other quantum technologies [5]. However, the implementation of optical quantum circuits with bulk optics has reached practical limits. We have developed an integrated waveguide approach to photonic quantum circuits for high performance, miniaturisation and scalability [6]. Here we report high-fidelity silica-on-silicon integrated optical realisations of key quantum photonic circuits, including two-photon quantum interference and a controlled-NOT logic gate [7]. We have demonstrated controlled manipulation of up to four photons on-chip, including high-fidelity single qubit operations, using a lithographically patterned resistive phase shifter [8]. We have used this architecture to implement a small-scale compiled version of Shor's quantum factoring algorithm [9] and demonstrated heralded generation of tuneable four photon entangled states from a six photon input [10]. We have combined waveguide photonic circuits with superconducting single photon detectors [11]. We describe complex quantum interference behaviour in multi-mode interference devices with up to eight inputs and outputs [12], and quantum walks of correlated particles in arrays of coupled waveguides [13]. Finally, we give an overview of our recent work on fundamental aspects of quantum measurement [14,15] and single photon sources [16,17]. [1] T. D. Ladd, F. Jelezko, R. Laflamme, Y. Nakamura, C. Monroe, and J. L. OBrien, Nature 464, 45 (2010). [2] J. L. O'Brien, Science 318, 1567 (2007). [3] T. Nagata, R. Okamoto, J. L. O'Brien, K. Sasaki, and S. Takeuchi, Science 316, 726 (2007). [4] R. Okamoto, J. L. O'Brien, H. F. Hofmann, T. Nagata, K. Sasaki, and S. Takeuchi, Science 323, 483 (2009). [5] J.L.O'Brien, A.Furusawa, and J.Vuckovic, Nature Photon. 3, 687 (2009). [6] A. Politi, M. J. Cryan, J. G. Rarity, S. Yu, and J. L. O'Brien, Science 320, 646 (2008). [7] A. Laing, A. Peruzzo, A. Politi, M. R. Verde, M. Halder, T. C. Ralph, M. G. Thompson, and J. L. O'Brien, Appl. Phys. Lett. 97, 211109 (2010) [8] J. C. F. Matthews, A. Politi, A. Stefanov, and J. L. O'Brien, Nature Photon. 3, 346 (2009). [9] A. Politi, J. C. F. Matthews, and J. L. O'Brien, Science 325, 1221 (2009). [10] J. C. F. Matthews, A. Peruzzo, D. Bonneau, and J. L. O'Brien, arXiv:1005.5119 [11] C. M. Natarajan, A. Peruzzo, S. Miki, M. Sasaki, Z. Wang, B. Baek, S. Nam, R. H. Hadfield, and J. L. O'Brien, Appl. Phys. Lett. 96, 211101 (2010). [12] A. Peruzzo, A. Laing, A. Politi, T. Rudolph, and J. L. O'Brien, Nature Comm. in press; arXiv:1005.5119 [13] A. Peruzzo, M. Lobino, J. C. F. Matthews, N. Matsuda, A. Politi, K. Poulios, X.-Q. Zhou, Y. Lahini, N. Ismail, K. Worhoff, Y. Bromberg, Y. Silberberg, M. G. Thompson, and J. L. O'Brien, Science 329, 1500 (2009) [14] A. Laing, T. Rudolph, and J. L. O'Brien, Phys. Rev. Lett. 102, 160502 (2009). [15] X-Q Zhou, TC Ralph, P Kalasuwan, M Zhang, A Peruzzo, BP Lanyon, and JL OBrien arXiv:1006.2670 [16] J. P. Hadden, J. P. Harrison, A. C. Stanley-Clarke, L. Marseglia, Y.-L. D. Ho, B. R. Patton, J. L. OBrien, and J. G. Rarity, Appl. Phys. Lett. 97, 241901 (2010) [17] C. Xiong, G. D. Marshall, A. Peruzzo, M. Lobino, A. S. Clark, D.-Y. Choi, S. J. Madden, C. M. Natarajan, M. G. Tanner, R. H. Hadfield, S. N. Dorenbos, T. Zijlstra, V. Zwiller, M. G. Thompson, J. G. Rarity, M. J. Steel, B. Luther-Davies, B. J. Eggleton, J. L. O’Brien arXiv:1011.1688

CQT Colloquium by Carlton M. Caves, University of New Mexico

Title: Quantum-limited measurements: One physicist's crooked path from quantum optics to quantum information
Date/Time: 20-Aug, 04:00PM
Venue: CQT Seminar Room, S15-03-15

Abstract: We will first review the recent progress in atomic clocks operating in the microwave and optical domain of the electromagnetic spectrum. The second of the SI system of units is realized today with an accuracy of 3 10-16 by a number of laser cooled atomic fountains worldwide. Optical clocks have recently reached a frequency stability and accuracy in the 10-18 range [1] opening new perspectives for time keeping and fundamental tests. We will then present the status of the ACES mission of the European Space Agency scheduled for flight to the International Space Station from 2013 to 2015 [2]. ACES will embark a laser cooled cesium clock designed for microgravity operation (PHARAO ), an active hydrogen maser (SHM), and a high precision time transfer system operating in the microwave domain. This microwave link (MWL) will enable frequency comparisons between the space clocks and a network of ground based clocks belonging to worldwide metrology institutes and universities. The link is designed for obtaining a relative frequency resolution of 10-17 after a few days of measurement duration for intercontinental comparisons. In 2009-2010, all elements of the flight payload have successfully passed the Engineering Model tests and flight models are under construction. We will present the latest measurement results and flight model designs. In a second part we will describe tests of fundamental physical laws using ultra-stable clocks in space and on the ground that are planned for the ACES mission. An improved measurement of Einstein's gravitational red-shift will be made at the two parts per million level. By comparing clocks of different nature at the 10-17/year level, new limits will be obtained for the time variation of the fundamental constants of physics such as the fine structure constant alpha and the ratio of electron to proton mass. The ability to compare microwave and optical clocks using the recently developed frequency comb technique opens a wide range of possibilities in clock comparisons. Finally a new kind of relativistic geodesy based on the Einstein effect will provide information on the Earth geoid, complementing the recent determination obtained by space geodesy methods. References: [1]C. W. Chou, D. B. Hume, J. C. J. Koelemeij, D. J. Wineland, and T. Rosenband, Phys. Rev. Lett. 104, 070802 (2010) [2] L. Cacciapuotti, and C. Salomon, Eur. Phys. J. Special Topics, 172, 57 (2009)

CQT Colloquium by Christophe Salomon, Laboratoire Kastler Brossel, France

Title: Space Clocks and Fundamental Tests
Date/Time: 10-Aug, 04:00PM
Venue: CQT Seminar Room, S15-03-15

Abstract: We will first review the recent progress in atomic clocks operating in the microwave and optical domain of the electromagnetic spectrum. The second of the SI system of units is realized today with an accuracy of 3 10-16 by a number of laser cooled atomic fountains worldwide. Optical clocks have recently reached a frequency stability and accuracy in the 10-18 range [1] opening new perspectives for time keeping and fundamental tests. We will then present the status of the ACES mission of the European Space Agency scheduled for flight to the International Space Station from 2013 to 2015 [2]. ACES will embark a laser cooled cesium clock designed for microgravity operation (PHARAO ), an active hydrogen maser (SHM), and a high precision time transfer system operating in the microwave domain. This microwave link (MWL) will enable frequency comparisons between the space clocks and a network of ground based clocks belonging to worldwide metrology institutes and universities. The link is designed for obtaining a relative frequency resolution of 10-17 after a few days of measurement duration for intercontinental comparisons. In 2009-2010, all elements of the flight payload have successfully passed the Engineering Model tests and flight models are under construction. We will present the latest measurement results and flight model designs. In a second part we will describe tests of fundamental physical laws using ultra-stable clocks in space and on the ground that are planned for the ACES mission. An improved measurement of Einstein's gravitational red-shift will be made at the two parts per million level. By comparing clocks of different nature at the 10-17/year level, new limits will be obtained for the time variation of the fundamental constants of physics such as the fine structure constant alpha and the ratio of electron to proton mass. The ability to compare microwave and optical clocks using the recently developed frequency comb technique opens a wide range of possibilities in clock comparisons. Finally a new kind of relativistic geodesy based on the Einstein effect will provide information on the Earth geoid, complementing the recent determination obtained by space geodesy methods. References: [1]C. W. Chou, D. B. Hume, J. C. J. Koelemeij, D. J. Wineland, and T. Rosenband, Phys. Rev. Lett. 104, 070802 (2010) [2] L. Cacciapuotti, and C. Salomon, Eur. Phys. J. Special Topics, 172, 57 (2009)

CQT Colloquium by Wolfgang Behr, University of Zurich, Switzerland

Title: Ciphering Classical Chinese
Date/Time: 05-Feb, 04:00PM
Venue: CQT Seminar Room, S15-03-15

Abstract: Once premodern European and Arabic cipherers started to leave the more pedestrian "physical" approaches to steganography behind, techniques of encryption in political, military, religious or private contexts consisted mainly in the transformative manipulation of a plaintext and the devision of adequate decoding keys. They were thus by and large tantamount to the evolution of ever more powerful mapping algorithms, and dependent on increasingly sophisticated insights into the distributional properties of letters and lexical roots occuring in alphabetically represented written language. In China, the topic of information secrecy has been discussed since the pre-imperial period. State institutions maintaining certain types of government information secret and laws regulating the punishment of its leakage were of great complexity already during the Qin and Han dynasties, and reached unsurpassed bureaucratic intricacies under the Ming. Nevertheless, actual coding procedures seem to have developed quite slowly throughout imperial Chinese history, in the public as well as the private sectors. After a short overview of the earliest anecdotal evidence related to the disguising of information in early Chinese military texts, my talk will concentrate on three techniques, which illustrate the difficulty of pre-modern encryption on the basis of a logographic writing system representing a largely monosyllabic, tonal language. These are (1) the so-called "character verification" method, described in the Northern Song Essentials from the Military classics by Zeng Gongliang (999-1078), which maps numbered military commands onto sequences of characters appearing in a memorized pentasyllabic poem, serving as the key; (2) a system inspired by the phonological categories of the Middle Chinese rhyme dictionary tradition, and ascribed to the famous anti-Japanese Ming general Qi Jiguang (1528-1588); (3) homophonic substitution and “synthanalytic” character manipulation in poetry and edicts, recorded, e.g. in documents from the Taiping rebellion. In a concluding discussion, the inhibitive role of the non-alphabetic writing system in the development of formalized coding procedures will be weighed against the influence, which the “non-development of probabilistic thinking“, i.e. the “lack of an exploratory serious playfulness“ (Mark Elvin) in China might have brought about.

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