Quantum Mechanical Effects in Ordinary Objects: Nanomechanics Coupled to Qubits

Michael L. Roukes of California Institute of Technology [photo credit: Pasi Jalkanen, University of Jyväskylä, Finland]

In a paper recently published in 'Nature', a team of scientists led by Michael Roukes of Caltech reported an interesting experiment coupling a superconducting qubit to a nanomechanical resonator -- which could provide a good insight into the quantum-mechanical behavior in ordinary objects.

At the quantum level, the atoms that make up matter and the photons that make up light behave in a number of seemingly bizarre ways. Particles can exist in "superposition", in more than one state at the same time (as long as we don't 'observe'), a situation that permitted Schrödinger's famed cat to be simultaneously alive and dead; matter can be "entangled" — Albert Einstein called it "spooky action at a distance" — such that one thing influences another thing, regardless of how far apart the two are.

Matt LaHaye

Previously, scientists have successfully measured entanglement and superposition in photons and in small collections of just a few atoms. But physicists have long wondered if larger collections of atoms — those that form objects with sizes closer to what we are familiar with in our day-to-day life — also exhibit quantum effects. [Read 'entanglement' related articles in 2Physics category: Quantum Computation & Communication].

"Atoms and photons are intrinsically quantum mechanical, so it's no surprise if they behave in quantum mechanical ways. The question is, do these larger collections of atoms do this as well," says Matt LaHaye, the lead author of the paper.

Keith Schwab [photo courtesy: kschwabresearch.com]

Keith Schwab, co-author of the paper, added,"It'd be weird to think of ordinary matter behaving in a quantum way, but there's no reason it shouldn't. If single particles are quantum mechanical, then collections of particles should also be quantum mechanical. And if that's not the case — if the quantum mechanical behavior breaks down — that means there's some kind of new physics going on that we don't understand."

The tricky part, however is devising an experiment that can detect quantum mechanical behavior in such ordinary objects — without, for example, those effects being interfered with or even destroyed by the experiment itself. Now, however, LaHaye, Schwab, Roukes, and their colleagues have developed a new tool that meets such fastidious demands and that can be used to search for quantum effects in an ordinary object.

In their experiment, the Caltech scientists used microfabrication techniques to create a very tiny nanoelectromechanical system (NEMS) resonator, a silicon-nitride beam — just 2 micrometers long, 0.2 micrometers wide, and weighing 40 billionths of a milligram — that can resonate, or flex back and forth, at a high frequency when a voltage is applied.

A small distance (300 nanometers, or 300 billionths of a meter) from the resonator, the scientists fabricated a second nanoscale device known as a single-Cooper-pair box, or superconducting "qubit" (a qubit is the basic unit of quantum information).

Scanning electron micrograph of a superconducting qubit in close proximity to a nanomechanical resonator. The nanoresonator is the bilayer (silicon nitride/aluminum) beam spanning the length of the trench in the center of the image; the qubit is the aluminum island located to the left of the nanoresonator. An aluminum electrode, located adjacent to the nanoresonator on the right, is used to actuate and sense the nanoresonator's motion. [Image credit: Junho Suh. Electron beam lithography was performed by Richard Muller at Jet Propulsion Laboratory. Nanoresonator etch was performed by Junho Suh in the Roukes Lab.]

The superconducting qubit is essentially an island formed between two insulating barriers across which a set of paired electrons can travel. In the Caltech experiments, the qubit has only two quantized energy states: the ground state and an excited state. This energy state can be controlled by applying microwave radiation, which creates an electric field.

Because the NEMS resonator and the qubit are fabricated so closely together, their behavior is tightly linked; this allows the NEMS resonator to be used as a probe for the energy quantization of the qubit. "When the qubit is excited, the NEMS bridge vibrates at a higher frequency than it does when the qubit is in the ground state", LaHaye says.

One of the most exciting aspects of this work is that this same coupling should also enable measurements to observe the discrete energy levels of the vibrating resonator that are predicted by quantum mechanics, the scientists say. This will require that the present experiment be turned around (so to speak), with the qubit used to probe the NEMS resonator. This could also make possible demonstrations of nanomechanical quantum superpositions and Einstein's spooky entanglement

"Quantum jumps are, perhaps, the archetypal signature of behavior governed by quantum effects," says Michael Roukes. "To see these requires us to engineer a special kind of interaction between our measurement apparatus and the object being measured. Matt's results establish a practical and really intriguing way to make this happen."

Reference
"Nanomechanical measurements of a superconducting qubit",
M. D. LaHaye, J. Suh, P. M. Echternach, K. C. Schwab, M. L. Roukes,
Nature 459, 960-964 (18 June 2009). Abstract.

[We thank Media Relations, Caltech for materials used in this posting]

Beam Pulses Perforate Black Hole Horizon

Alexander Burinskii


[Every year (since 1949) the Gravity Research Foundation honors best submitted essays in the field of Gravity. This year's prize goes to Alexander Burinskii for his essay "Instability of Black Hole Horizons with respect to Electromagnetic Excitations". The five award-winning essays will be published in the Journal of General Relativity and Gravitation (GRG) and subsequently, in a special issue of the International Journal of Modern Physics D (IJMPD). Today we present here an invited article from Prof. Burinskii on his current work.
-- 2Physics.com ]



Author: Alexander Burinskii
Nuclear Safety Institute, Russian Academy of Sciences, Moscow, Russia

The variety of models of the black-hole (BH) evaporation process -- that appeared in recent years -- differ essentially from each other, as well as from Hawking’s original idea. However, they contain a common main point that the mechanism of evaporation is connected with a complex analyticity and conformal structure [1], which unifies the BH physics with (super)string theory and physics of elementary particles [2, 3].

It has been observed long ago that many exact solutions in gravity contain singular wires and beams. Looking for exact wave solutions for electromagnetic (EM) field on the Kerr-Schild background, we obtained results [4] which show that they do not contain the usual smooth harmonic functions, but acquire commonly singular beam pulses which have very strong back reaction to metric. Analysis showed [5] that the EM beams break the BH horizon, forming the holes connecting the internal and external regions. As a result, the horizon of a BH interacting with the nearby EM fields turns out to be covered by a set of holes [6, 7] and will be transparent for outgoing radiation. Therefore, the problem of BH evaporation acquires explanation at the classical level.

2Physics articles by past winners of the Gravity Research Foundation award:
T. Padmanabhan (2008): "Gravity : An Emergent Perspective"
Steve Carlip (2007): "Symmetries, Horizons, and Black Hole Entropy"

We consider BH metric in the Kerr-Schild (KS) form [8]: g_μν = η_μν + 2H k_μ k_ν, which has many advantages. In particular, the KS coordinate system and solutions do not have singularities at the horizon, being disconnected from the positions of the horizons and rigidly related with auxiliary Minkowski space-time with metric η_μν. The Kerr-Schild form is extremely simple and all the intricate details are encoded in the vortex vector field k_μ(x) which is tangent to the light-like rays of the Kerr Congruence (in fact, these rays are twistors of the Penrose twistor theory).

The vector field k_ν determines symmetry of space, its polarization, and in particular, direction of gravitational ‘dragging‘. The structure of Kerr congruence is shown in Fig.1.

FIG. 1: The Kerr singular ring and Kerr congruence formed by the light-like twistor-beams.

Horizons are determined by function:
H =(mr − ψ²)/(r² + a² cos²θ) , where the function ψ ≡ ψ(Y) is related with electromagnetic field, and can be any analytic function of the complex angular coordinate
Y= exp{iφ} tan(θ/2) which parametrizes celestial sphere. The Reference [8] showed that the Kerr-Newman solution is the simplest solution of the Kerr-Schild class having ψ = q =constant, the value of charge. However, any holomorphic function ψ(Y ) also leads to an exact solution of this class, and such a non-constant function on sphere has to acquire at least one pole which creates the beam. So, the electromagnetic field corresponding to ψ(Y ) = q / Y forms a singular beam along z-axis which pierces the horizons, producing a hole allowing matter to escape the interior of black hole. The initially separated external and internal surfaces of the event horizons, r₊ and r_-, turn out to be joined by a tube, conforming a single connected surface.

This solution may be easily extended to the case of arbitrary numbers of beams propagating in different angular directions Y_i = exp{i φ_i} tan(θ_i/2) , which corresponds to a set of the light-like beams destroying the horizon in different angular directions, via action of the function ψ(Y) in H. The solutions for wave beams have to depend on a retarded-time τ. Their back reaction to the metric is especially interesting. Some long-term efforts [4, 6, 7] led us to obtain such solutions of the Debney-Kerr-Schild equations [8] in the low-frequency limit, and finally, obtain the exact solutions consistent with a time-averaged stress-energy tensor [9]. These time-dependent solutions revealed a remarkable structure which sheds light on the possible classical explanation of the BH evaporation, namely, a classical analog of quantum tunneling. In the exact time-dependent solutions, a new field of radiation was obtained which is determined by regular function γ_(reg)(Y,τ). This radiation is akin to the well known radiation of the Vaidya `shining star' and may be responsible for the loss of mass by evaporation. At the same time, the necessary conditions for evaporation -- the transparence of the horizon -- are provided by the singular field ψ(Y,τ) forming the fluctuating beam-pulses. As a result, the roles of ψ(Y,τ) and γ_(reg)(Y,τ) are separated! The horizon turns out to be fluctuating and pierced by a multitude of migrating holes, see Fig. 2.

The obtained solutions showed that the horizon is not irresistible obstacle, and there should not be any information loss inside the black hole. Due to topological instability of the horizon, the black-holes lose their demonic image, and hardly they can be created in a collider. However, the usual scenarios of the collapse have to be apparently valid, since the macroscopic processes should not be destroyed by the fine-grained fluctuations of the horizon. The known twosheetedness of the Kerr metric, which was considered as a long time mystery of the Kerr solution, turns out to be matched perfectly with the holographic structure of space-time [9,10]. The resulting classical geometry produced by fluctuating twistor-beams may be considered as a fine-grained structure which takes an intermediate position between the classical and quantum gravity [9].

References:
[1] S. Carlip, "Black Hole Entropy and the Problem of Universality",
J. Phys. Conf. Ser.67: 012022, (2007), gr-qc/0702094.
[2] G. `t Hooft, "The black hole interpretation of string theory",
Nucl Phys. B 335, 138 (1990). Abstract.
[3] A. Burinskii, "Complex Kerr geometry, twistors and the Dirac electron",
J. Phys A: Math. Theor, 41, 164069 (2008). Abstract. arXiv: 0710.4249[hep-th].
[4] A. Burinskii, "Axial Stringy System of the Kerr Spinning Particle",
Grav. Cosmol. 10, (2004) 50, hep-th/0403212.
[5] A. Burinskii, E. Elizalde, S.R. Hildebrandt and G. Magli, "Rotating 'black holes' with holes in the horizon", Phys. Rev. D 74, 021502(R) (2006) Abstract; A. Burinskii, "The Kerr theorem, Kerr-Schild formalizm and multiparticle Kerr-Schild solutions", Grav. Cosmol. 12, 119 (2006), gr-qc/0610007.
[6] A. Burinskii, "Aligned electromagnetic excitation of the Kerr-Schild Solutions",
Proc. of MG12 (2007), arXiv: gr-qc/0612186.
[7] A. Burinskii, E. Elizalde, S.R. Hildebrandt and G. Magli,"Aligned electromagnetic excitations of a black hole and their impact on its quantum horizon", Phys.Lett. B 671 486 (2009). Abstract.
[8] G.C. Debney, R.P. Kerr and A.Schild, "Solutions of the Einstein and Einstein-Maxwell Equations",
J. Math. Phys. 10, 1842 (1969). Abstract.
[9] A. Burinskii, "Beam Pulse Excitations of Kerr-Schild Geometry and Semiclassical Mechanism
of Black-Hole Evaporation", arXiv:0903.2365 [hep-th] .
[10] C.R. Stephens, G. t' Hooft and B.F. Whiting, "Black hole evaporation without information loss", Class. Quant. Grav. 11, 621 (1994). Abstract.

World’s Fastest Continuously Running Camera

Kevin K. Tsia, Bahram Jalali, and Keisuke Goda (from Left to Right)

[This is an invited article based on a recent work of the authors -- 2Physics.com]

Authors: Keisuke Goda, Kevin K. Tsia, and Bahram Jalali

Affiliation: Photonics Laboratory, Department of Electrical Engineering, University of California, Los Angeles.

Photonics.ucla.edu


Continuous real-time imaging technology with high temporal resolution is required for studying rapid dynamical phenomena such as shockwaves, chemical dynamics in living cells, neural activity, laser surgery, and microfluidics. However, traditional electronic image sensors such as CCD and CMOS cameras are unable to capture such processes with high sensitivity and resolution. This is partly due to the technological limitation that it takes time to read out the data from the sensor array, and also due to the fundamental trade-off between speed and sensitivity; at high frame rates, fewer photons are collected during each frame – a predicament that affects virtually all optical imaging systems.

Past 2Physics article by Keisuke Goda and his collaborators:
"Beating the Quantum Limit in Gravitational Wave Detectors"

To overcome these limitations, we have proposed and demonstrated a new type of imaging technique that offers at least 1000 times higher frame rates than traditional electronic image sensors such as CCDs [1]. This imaging method, which we refer to as serial time-encoded amplified imaging or microscopy (STEAM), is an extension of our ultrafast 1D imager [2]. It maps the 2D image of an object into a serial time-domain data stream and simultaneously amplifies the image in the optical domain using the technique known as amplified dispersive Fourier transformation. It captures the 2D image, not with a CCD camera, but with a single-pixel photodiode. The main attributes of the STEAM camera are the optical image amplification and the elimination of the CCD. When combined, it achieves continuous real-time imaging at a record frame rate of more than 6 MHz and a shutter speed of 440 ps. Achieving an image gain of 25 dB, the STEAM camera overcomes the fundamental trade-off between speed and sensitivity without having to resort to cooling and high-intensity illumination. The STEAM camera operates continuously and can capture ultrafast dynamical processes without any knowledge of the timing of their occurrence.

Movie 1: Animated movie that illustrates the functionality of the STEAM camera.

The details of the STEAM camera’s operation are shown in Movie 1. A broadband pulse is dispersed and separated by a pair of dispersive elements consisting of a virtually-imaged phased array and a diffraction grating to produce a 2D rainbow. When this is incident onto the object, the spatial coordinates of the object are encoded into the spectrum of the back-reflected 2D rainbow. The key innovation is what happens next. The reflected pulse is directed toward an amplified dispersive Fourier transformer which maps the image-encoded spectrum into a 1D temporal data stream, and simultaneously amplifies the image using distributed Raman amplification. The optically amplified 1D serial data is detected by a single-pixel photodiode and digitized by a real-time oscilloscope. The 2D image of the object is reconstructed by folding the 1D vector into a 2D matrix, representing the 2D image, in the digital domain.

The image amplifier in the STEAM camera is different from so-called image intensifiers. In the STEAM camera, amplification occurs in the optical domain as opposed to in the electronic domain in image intensifiers. Image intensifiers are complex devices and have a low image acquisition rate up to ~10 kHz in continuous mode – performance that is adequate for its intended use in night-vision cameras because they only need to operate at the video rate. The limited frame rate is due to the fundamental trade-off between gain and bandwidth in all electronic systems, including the image intensifier.

In scientific applications, high-speed imaging is often achieved with the time-resolved pump-probe technique [3]. Pump-probe techniques can capture the dynamics of fast events, but only if the event is repetitive. Because they do not operate in real time, they are unable to capture non-repetitive random events that occur only once or do not occur at regular intervals such as rogue events [4]. Detection of such events requires an imaging technology with fast, continuous, and real-time capability.

Another type of high-speed image sensor is the framing streak camera that has been employed for diagnostics in laser fusion, plasma radiation and combustion. This device operates in burst mode only (providing only several frames) and requires synchronization of the camera with the event to be captured, rendering streak cameras also unable to capture unknown or random events. This, along with the high cost of the camera, limits its use in practical applications.

Figure 2: [Click to see a better resolution image]
Continuous real-time images of the laser ablation experiment. Continuous real-time images captured by the STEAM camera with a temporal resolution of 163 ns and shutter speed of 440 ps. The changes in sample surface reflectivity due to the laser-induced mass ejection are evident after the ablation pulse hits the sample at t = 0 ns.

To demonstrate the STEAM camera’s ultrafast real-time imaging capability and utility, we have used it to successfully capture the dynamics of laser ablation. Laser ablation is a ubiquitous technology that is used in laser surgery, laser cutting and micromachining, and laser-induced breakdown spectroscopy. The ablation was performed with a mid-infrared pulse with 5 ns pulse width focused at an angle onto a sample consisting of a bilayer of aluminum and silicon dioxide deposited on top of a silicon-on-insulator substrate. The imaging pulse train of the STEAM camera was incident to the surface of the sample at a normal angle. Figure 2 shows the real-time sequence of the images with a frame repetition period of 163 ns. The entire frame sequence corresponding to the dynamics (laser-induced mass ejection) caused by the single ablation pulse was captured in real time.

Reference
[1] “Serial time-encoded amplified imaging for real-time observation of fast dynamic phenomena", K. Goda, K. K. Tsia, and B. Jalali, Nature 458, 1145 (2009). Abstract.
[2] “Amplified dispersive Fourier-transform imaging for ultrafast displacement sensing and barcode reading”, K. Goda, K. K. Tsia, and B. Jalali, Applied Physics Letters 93, 131109 (2008). Abstract.
[3] “Ultrafast single-shot diffraction imaging of nanoscale dynamics”, A. Barty, S. Boutet, M. J. Bogan, S. Hau-Riege, S. Marchesini, K. Sokolowski-Tinten, N. Stojanovic, R. Tobey, H. Ehrke, A. Cavalleri, S. Düsterer, M. Frank, S. Bajt, B. W. Woods, M. M. Seibert, J. Hajdu, R. Treusch & H. N. Chapman,
Nature Physics 2, 415 (2008). Abstract.
[4] “Optical rogue waves,” D. R. Solli, C. Roper, P. Koonath, and B. Jalali,
Nature 450, 1054 (2007). Abstract.

Large Broadband Invisibility Cloak for Visible Light

Vera Smolyaninova (Towson University)


[This is an invited article based on recent work of the authors. -- 2Physics.com]

Authors: Vera Smolyaninova¹ and Vlad Shalaev<sup>2

1</sup>Dept. of Physics Astronomy and Geosciences, Towson University, Towson, MD, USA

²Birck Nanotechnology Center, School of Electrical and Computer Engineering, Purdue University, West Lafayette, IN, USA


Most researchers believe that sophisticated artificially engineered materials are required to build an invisibility cloak. Such “metamaterials” exhibit high losses and work for only one color. The resulting invisibility cloaks are tiny, and cannot hide anything if another color of light is used. Our team, Igor Smolyaninov from BAE Systems, Vera Smolyaninova from Towson University, Alexander Kildishev and Vlad Shalaev form Purdue University demonstrated a different approach to cloaking.

Vlad Shalaev (Purdue University)

Instead of sophisticated metamaterials, we used a waveguide, which is curved to mimic the metamaterial properties. This approach leads to all-color invisibility cloak with much lower losses. As a result, we built a large optical cloak, which is about hundred times larger than the cloaks built previously. This “see-through” cloak bends light around itself and thus differs from the “invisibility carpet,” which camouflages bumps on a metal surface. We believe that further size increase is possible, and that the same technique may be applied to other tasks, which require the use of metamaterials, such as building new “hyperlenses” which considerably surpass the resolution limit of conventional lenses.

This work is reported in the May 29 issue of Physical Review Letters [1]. In the experiments, conducted at Towson University, electromagnetic cloaking is achieved using a specially tapered waveguide. An area with a radius ~100 times larger than the wavelengths of light shined by a laser into the device has been cloaked, an unprecedented achievement. This is the first experiment on optical cloaking performed with normal visible light.

Previous experiments with metamaterials, which require complex nanofabrication, have been limited to cloaking regions only a few times larger than the wavelengths of visible light [2,3]. The new design is a far simpler device: waveguides represent established technology - including fiber optics - used in communications and other commercial applications. Because the new method enabled us to dramatically increase the cloaked area, the technology offers hope of cloaking larger objects. All previous attempts at optical cloaking have involved very complicated nanofabrication of metamaterials containing many elements, which makes it very difficult to cloak large objects. Here, we showed that if a waveguide is tapered properly it acts like a sophisticated nanostructured material. The waveguide is inherently broadband, meaning it could be used to cloak the full range of the visible light spectrum. Unlike metamaterials, which contain many light-absorbing metal components, only a small portion of the new design contains metal.

Igor Smolyaninov (BAE Systems)

Theoretical work for the design was led by Purdue, with BAE Systems and Towson University leading work to fabricate the device and demonstrate its cloaking properties. The cloaking device is formed by two gold-coated surfaces, one a curved lens and the other a flat sheet. We cloaked an object about 50 microns in diameter, or roughly the width of a human hair, in the center of the waveguide. Instead of being reflected as normally would happen, the light flows around the object and shows up on the other side, like water flowing around a stone.

This research falls within a new field called transformation optics, which may usher in a host of radical advances, including cloaking; powerful "hyperlenses" resulting in microscopes 10 times more powerful than today's and able to see objects as small as DNA; computers and consumer electronics that use light instead of electronic signals to process information; advanced sensors; and more efficient solar collectors.

Alexander Kildishev (Purdue University)

Unlike natural materials, metamaterials are able to reduce the "index of refraction" to less than one or less than zero. Refraction occurs as electromagnetic waves, including light, bend when passing from one material into another. It causes the bent-stick-in-water effect, which occurs when a stick placed in a glass of water appears bent when viewed from the outside. Each material has its own refraction index, which describes how much light will bend in that particular material and defines how much the speed of light slows down while passing through a material. Natural materials typically have refractive indices greater than one. Metamaterials, however, can be designed to make the index of refraction vary from zero to one, which is needed for cloaking. The precisely tapered shape of the new waveguide alters the refractive index in the same way as metamaterials, gradually increasing the index from zero to 1 along the curved surface of the lens. Previous cloaking devices have been able to cloak only a single frequency of light, meaning many nested devices would be needed to render an object invisible.

We reasoned that the same nesting effect might be mimicked with the waveguide design. Subsequent experiments and theoretical modeling proved the concept correct. We do not know of any fundamental limit to the size of objects that could be cloaked, but additional work will be needed to further develop the technique.

Recent cloaking findings reported by researchers at other institutions have concentrated on a technique that camouflages features against a background. Those works, which use metamaterials, are akin to rendering bumps on a carpet invisible by allowing them to blend in with the carpet, whereas our work concentrates on enabling light to flow around an object.

The work was funded by the ARO-MURI and the National Science Foundation.

References
[1] “Anisotropic metamaterials emulated by tapered waveguides: application to electromagnetic cloaking”, I.I. Smolyaninov, V.N. Smolyaninova, A.V. Kildishev, and V.M. Shalaev,
Phys. Rev. Letters, 102, 213901 (2009). Abstract.
[2] “Metamaterial electromagnetic cloak at microwave frequencies”, D. Schurig, J.J. Mock, B.J. Justice, S.A. Cummer, J.B. Pendry, A.F. Starr, D.R. Smith, , Science 314, 977-980 (2006). Abstract.
[3] “Two-dimensional metamaterial structure exhibiting reduced visibility at 500 nm”, I.I. Smolyaninov, Y.J. Hung, and C.C. Davis, Optics Letters 33, 1342-1344 (2008). Abstract.