Creation spontanée de lumière

[jgricourt]

Vous connaissiez peut être l'effet Casimir et bien maintenant voici l'effet effet Casimir dynamique ! Cet effet surprenant de la physique quantique prédit par le physicien américain Gerald Moore en 1970 viens d'être observé dans une expérience mettant un miroir en mouvement à 25% de la vitesse de la lumière. Le miroir se met alors à émettre spontanément des photons ...

 

Des physiciens créent de la lumière à partir du vide

 

PS: je sais ce journal n'est pas très scientifique mais je suis tombé dessus par hasard, si d'autres ont des infos pour éclairer le propos alors n'hésitez surtout pas !

[jujulolo]

J'ai accès a l'article de Nature en pdf si ca interesse quelqu'un.

 

Nature | Letter

 

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Observation of the dynamical Casimir effect in a superconducting circuit

 

C. M. Wilson,

G. Johansson,

A. Pourkabirian,

M. Simoen,

J. R. Johansson,

T. Duty,

F. Nori

& P. Delsing

 

Affiliations

Contributions

Corresponding author

 

Nature

479,

376–379

(17 November 2011)

doi:10.1038/nature10561

 

Received

31 August 2011

Accepted

15 September 2011

Published online

16 November 2011

 

 

 

JE recopie l'abstract:

 

One of the most surprising predictions of modern quantum theory is that the vacuum of space is not empty. In fact, quantum theory predicts that it teems with virtual particles flitting in and out of existence. Although initially a curiosity, it was quickly realized that these vacuum fluctuations had measurable consequences—for instance, producing the Lamb shift1 of atomic spectra and modifying the magnetic moment of the electron2. This type of renormalization due to vacuum fluctuations is now central to our understanding of nature. However, these effects provide indirect evidence for the existence of vacuum fluctuations. From early on, it was discussed whether it might be possible to more directly observe the virtual particles that compose the quantum vacuum. Forty years ago, it was suggested3 that a mirror undergoing relativistic motion could convert virtual photons into directly observable real photons. The phenomenon, later termed the dynamical Casimir effect4, 5, has not been demonstrated previously. Here we observe the dynamical Casimir effect in a superconducting circuit consisting of a coplanar transmission line with a tunable electrical length. The rate of change of the electrical length can be made very fast (a substantial fraction of the speed of light) by modulating the inductance of a superconducting quantum interference device at high frequencies (>10 gigahertz). In addition to observing the creation of real photons, we detect two-mode squeezing in the emitted radiation, which is a signature of the quantum character of the generation process.

[jujulolo]

Le news and views de cet article:

 

Nature | News & Views

 

Quantum physics: Shaking photons out of the vacuum

 

Diego A. R. Dalvit

 

Nature

479,

303–304

(17 November 2011)

doi:10.1038/479303a

 

Published online

16 November 2011

 

The dynamical Casimir effect — the generation of photons out of the quantum vacuum induced by an accelerated body — has been experimentally demonstrated using a superconducting circuit that simulates a moving mirror.

 

Quantum theory predicts that the vacuum of space is a roiling bath of virtual particles that continuously appear and disappear. These vacuum fluctuations produce measurable phenomena, such as the Casimir effect1, which arises from the pressure that virtual photons exert on stationary bodies. In 1970, Gerald Moore2 theorized that bodies in accelerated motion would produce real photons out of quantum vacuum fluctuations — the dynamical Casimir effect. In this issue (page 376), Wilson et al.3 report the first experimental demonstration of the dynamical Casimir effect, using a superconducting circuit that simulates an oscillating mirror.

 

Accelerated bodies modify quantum vacuum fluctuations, causing emission of photon pairs from the vacuum4 and dissipation of the bodies' motional energy. The power dissipated in the motion of the body is equal to the total radiated electromagnetic power, as expected according to the law of energy conservation. In its original form, the dynamical Casimir effect was predicted to occur when a single mechanical mirror undergoes accelerated motion in the vacuum. It was then extended to configurations in which the photon production rate is enhanced; for example, in cavities formed by two parallel mirrors, where the position of one of them oscillates with time.

 

A serious problem for detecting the dynamical Casimir effect induced by moving mechanical systems is that the dissipated energy and the associated radiation are negligibly small. Among other requirements, motions at nearly the speed of light are necessary. Because of these difficulties, several analogous systems have been proposed for observing the effect, the first being a nonlinear optical medium whose refractive index is rapidly changed with time5.

 

In one experiment being pursued6, the moving mirror is simulated by a semiconducting, layered wall whose conductivity is periodically modulated by an external laser; this set-up closely resembles an actual oscillating mirror. Wilson and colleagues' experiment3 is based on another proposal7, and consists of a waveguide terminated at one end by a superconducting quantum interference device (SQUID) — a very sensitive magnetometer. In this approach, a time-dependent magnetic flux threading through the SQUID modifies the electromagnetic field in the waveguide, just as if the SQUID had been replaced by a moving mirror. Because there is no massive body in motion, the effective velocity of the fictitious mirror can be made a substantial fraction of the speed of light.

 

Even without the dynamical Casimir effect, photons can exist at any finite temperature, and these must be distinguished from motion-induced photons generated from the vacuum. By cooling their apparatus to very low temperatures (less than about 50 millikelvin), Wilson et al. prepared their system as close as possible to the vacuum state — the number of thermal photons remaining in such a cold environment is very small. To produce dynamical Casimir photons, the authors 'pumped' the system with a time-varying magnetic flux through the SQUID. They then measured the intensity and frequency of the generated radiation at the open end of the waveguide, as a function of the strength and frequency of the pump field.

 

Wilson et al. detected motion-induced radiation whose broadband microwave energy spectrum was symmetrical at around half the frequency of the oscillating fictitious mirror. The measured spectrum is consistent with that of dynamical Casimir photons, which are generated in pairs whose frequencies add up to the mirror's oscillation frequency. What's more, they found that the measured photon intensity versus pump strength compares reasonably well with theoretical predictions. In addition to observing the creation of real photons, Wilson and colleagues measured photon correlations in the output port of their system. To do this, they split the output photon signal into two separate analysis chains and detected specific correlations. Such correlations are a signature of the quantum nature of the photon-generation process and are another hallmark of the dynamical Casimir effect.

 

A potential problem with these measurements is that photons might be generated by spurious processes that could mimic the dynamical Casimir effect. Wilson and colleagues considered, and ruled out, a number of such systematic effects. For example, nonlinearities in the electromagnetic properties of the waveguide's substrate and/or in the SQUID electronics could conceivably generate photons in the output port by means of a process known as parametric down-conversion. But the authors emphasize that the pump-power levels used in their experiment are much lower than those needed for such nonlinear processes to occur. Even in the absence of spurious nonlinear mechanisms, motion-induced photons could be seeded, not by quantum vacuum fluctuations, but by uncontrolled noise in the apparatus (for example, thermal noise). However, the authors measured the output photon flux at two temperatures (50 and 250 mK) and were able to verify that the signals are dominated by quantum, and not thermal, fluctuations.

 

Wilson and colleagues' breakthrough demonstration of the dynamical Casimir effect, together with other ongoing experimental and theoretical efforts, will strongly impact on fundamental physics. They will enable table-top demonstrations of particle creation in an expanding Universe and of black-hole evaporation, among others.

[Dr Eric Simon]

Génial ! Je connaissais pas cet effet Casimir inverse. En gros, le vide freine les trucs qui vibrent à des vitesses proches de c en émettant des paires de photons.

 

Faut qu'on arrête d'appeler ça le "vide", c'est un peu faux

[jgricourt]

Oui on l'appel le vide "quantique" tout ça un peu à cause de l'inégalité d'Heisenberg !

[iksarfighter]

Peut-être la cause de la vitesse limite c à laquelle semblent soumis tous les objets de notre univers ?

[jarnicoton]

Ou un corollaire.