Then the photons with horizontal polarization pass through the polarization beam splitter and encounter the filter. Firstly the photons encounter the Stokes-resonant cavity, the Stokes photons pass through the Stokes-resonant cavity, but the anti-Stokes photons are reflected by the front surface of the Stokes-resonant cavity. Then, the reflected anti-Stokes photons pass through the quarter-wave plate again. Note that, double pass of a quarter-wave plate is equivalent to a half-wave plate.
The anti-Stokes photons therefore flip its polarization to vertical and reflected by the polarization beam splitter, and finally pass through the anti-Stokes-resonant cavity. We can see that the Stokes photons and anti-Stokes photons pass through different set of cavities, respectively. The transmission windows of cavities shown in Fig. Single photons are not the best choice for measuring transmission windows of cavities since the fluctuations of single photons and ambient noise will bring considerably difficulty to adjust and optimize the cavities.
On the other hand, high intensive light is also not suitable since the cavities will be warmed by the intensive light and the transmission windows of cavities will shift away from their correct frequency position. The grey circles are experimental data and the green lines are fitting curves.
A broadband DLCZ quantum memory in room-temperature atoms
The grey columns are experimental data and the blue lines are fitting curves. If function S f is assumed to be the frequency spectra of Stokes photons or anti-Stokes photons, then. The spectra are shown in Fig. The data that support the findings of this study are available from the corresponding author on reasonable request. Photonic quantum technologies. Jin, X. Experimental free-space quantum teleportation.
Gisin, N. Quantum communication. Ladd, T. Quantum computers. Nature , 45—53 Aspuru-Guzik, A. Photonic quantum simulators. Lvovsky, A. Optical quantum memory. Briegel, H. Quantum repeaters: the role of imperfect local operations in quantum communication. Duan, L.
Long-distance quantum communication with atomic ensembles and linear optics. Nature , — Nunn, J. Enhancing multiphoton rates with quantum memories. Storage and retrieval of single photons transmitted between remote quantum memories. Eisaman, M. Electromagnetically induced transparency with tunable single-photon pulses.
Zhang, H. Preparation and storage of frequency-uncorrelated entangled photons from cavity-enhanced spontaneous parametric downconversion. Kuzmich, A. Generation of nonclassical photon pairs for scalable quantum communication with atomic ensembles. Chrapkiewicz, R. High-capacity angularly multiplexed holographic memory operating at the single-photon level.
Julsgaard, B. Experimental demonstration of quantum memory for light. Moiseev, S. Complete reconstruction of the quantum state of a single-photon wave packet absorbed by a Doppler-broadened transition. Alexander, A.
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Photon echoes produced by switching electric fields. Afzelius, M. Multimode quantum memory based on atomic frequency combs.
Reim, K. Multi-pulse addressing of a Raman quantum memory: configurable beam splitting and efficient readout.
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Ding, D. Raman quantum memory of photonic polarized entanglement. Manz, S. Collisional decoherence during writing and reading quantum states. Michelberger, P. Interfacing GHz-bandwidth heralded single photons with a warm vapour Raman memory. Lee, K. Entangling macroscopic diamonds at room temperature. Science , — England, D. Storage and retrieval of THz-bandwidth single photons using a room-temperature diamond quantum memory. Kaczmarek, K. High-speed noise-free optical quantum memory. Finkelstein, R. Fast, noise-free memory for photon synchronization at room temperature.
Clauser, J. Experimental distinction between the quantum and classical field-theoretic predictions for the photoelectric effect. D 9 , — Direct measurement of decoherence for entanglement between a photon and stored atomic excitation. Bao, X. Efficient and long-lived quantum memory with cold atoms inside a ring cavity. Quantum memory for photons. Today 68 , 42—47 Three-dimensional theory for interaction between atomic ensembles and free-space light.
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It can represent a beam sent to reflect on the moon to measure the latter's distance from the Earth, a light source injected into an optical fibre as a medium for information, or a train of short and intense pulses to probe chemical reaction dynamics or to initiate fusion of atomic nuclei. This presentation will therefore focus on one of the most spectacular and paradoxical applications of laser, namely: the cooling of atomic gases.
This is how quantum matter is produced, with radically different properties from those of the fluids or solids we encounter in daily life. Interest in this quantum matter extends far beyond the scope of atomic physics specialists. Physicists of condensed matter, chemists, mathematicians and astrophysicists all use it as a source of illustrations and research questions regarding phenomena related to their discipline.
Many professors at this institution have made their mark on the physics of light and atoms at the highest level. I will mention only a few prestigious names of scientists who forged this discipline. Finally, I would like to salute two great physicists and professors whom I was fortunate to know.
Through his study of nuclear magnetism, Anatole Abragam laid the foundations of a theory that extends to many physical phenomena, particularly to my own research field, quantum optics. Claude Cohen-Tannoudji was my PhD supervisor; he guided my first steps in research with extreme benevolence, and has done me honour and kindness of being here tonight. I would like to thank you, dear Serge Haroche, for having one day offered me this challenge and for supporting my candidacy before the Faculty, and all of you, dear colleagues, for putting your trust in me. This month of April is a special anniversary in the history of the evolution of ideas on the description of matter.
He was aware of their latest experimental discoveries: matter is composed of positively charged particles, atomic nuclei, in which the bulk of mass is concentrated, and far lighter negatively charged particles, electrons. All these particles occupy but an infinitely small fraction of space. Between the nucleus and the electrons, there is just emptiness, nothing but emptiness. The question that Bohr, like many other physicists, was grappling with was the surprising stability of the atomic structure.
What is it that prevents each electron from falling to the nucleus? Here are some of their values: In , Balmer noticed that these wavelengths could be written in a simple mathematical form, with a formula that was later completed by Rydberg and Ritz:. Bohr, convinced of the latter, based his reasoning on a planetary model of the atom, popularized by Jean Perrin some ten years earlier.
Any given atomic species — hydrogen, helium, lithium, etc. These two basic processes, photon absorption and emission, are the cornerstones of the interaction between matter and radiation. Process of absorption by an atom. To the right, the atom has absorbed the photon and has shifted to the energy state E 3.
In a gas, the movement of atoms or molecules is erratic and their thermal velocity increases with temperature. Thus the nitrogen and oxygen molecules that make up the ambient air have typical speeds of a few hundred metres per second and the temperature is about K. I here use the notion of absolute temperature, obtained by taking the usual temperature, measured in degrees Celsius, and adding Using absolute temperature is interesting, since it immediately shows the difference from complete rest, obtained at temperature zero.
With the invention and development of optical pumping, Alfred Kastler and Jean Brossel made a first step in that direction 4. These states are assumed to be stable, in the sense that an isolated atom, which has been prepared in State 1 or State 2, will definitively remain there. We then choose an initial configuration of our assembly such that the atoms are randomly distributed across one or the other of States 1 and 2. The disorder here consists of the fact that the state occupied by a given atom is unknown, and the aim is to make this element of randomness disappear.
This light will efficiently make the atoms of State 2 move to State 3, which has a higher energy. An atom occupying State 1 is however insensitive to this radiation: it will therefore remain there indefinitely. Optical pumping principle. At the top, an assembly of six atoms is randomly distributed across the energy states E 1 and E 2. The initial disorder has been removed. This state is chosen to be unstable, and the atom ends up dropping back down into State 1 or State 2 by emitting another photon.
If it drops into State 1 it stops there: this is the accumulation sought. If it drops into State 2, it will again absorb a photon, rise back up to State 3 and try again. After quite a while, the steering towards State 1 has occurred for all atoms: the initial disorder of the atomic assembly has been significantly reduced by means of light. In order to cool a gas, it is not enough to order the distribution of atoms across their internal energy state.
Starting with atoms going in all directions of space at different speeds, the aim is to bring them to a virtual standstill. Several methods have been implemented to do so and I will present one highly efficient such method, called Sisyphus cooling. Nevertheless, this scale is not completely fixed: when atoms are subjected to an electric or magnetic field, the position of the energy levels changes. This is also the case when light is shed on the atoms with a light beam, as Claude Cohen-Tannoudji showed in light can shift atomic energy levels upwards or downwards.
Suppose that these levels can be shifted by a light beam in opposite directions: the light shifts Level 1 slightly downwards and Level 2 slightly upwards. In the absence of light, the levels are closer together, and move away from each other when there is light. We focus light on them with a light beam propagating along this axis. Using a mirror, we send the beam back on itself. An interference phenomenon then produces a stationary wave. The atom starts off for instance by ascending a hill of potential associated with Level 2.
After reaching the top of the hill, the atom is in principle going to go down the other slope. But we can disrupt its course by resorting to optical pumping. More precisely, we can make sure that when the atom reaches the top of the hill, it is transferred to Level 1, where it finds itself at the bottom of a valley. The atom then ascends a second time, after which it arrives on top of a hill for Level 1. At this point, if well controlled, the optical pumping can bring the atom back towards Level 2, forcing it to climb a third hill in a row, and so on. The atom therefore goes through a series of ascents, until its energy is too weak to reach the following top and it remains trapped at the bottom of a valley.
Their initial kinetic energy has been taken away by the photons emitted during the optical pumping processes. We use the term optical molasses to describe this viscous environment created by the laser beam, in which the motion of atoms is slowed down like that of a spoon in a honey pot. Sisyphus cooling principle.
Physicists create record-setting quantum motion
In a stationary light wave, the energy levels are modulated in space. Configurations exist such that the atom constantly ascends hills of potential, with optical pumping placing it at the bottom of a valley as soon as it reaches a hilltop. When its energy becomes too weak, the atom is trapped at the bottom of a well of potential.
The temperatures measured on Earth, whether at a pole or by the equator, are very close to each other on that scale, between and kelvins. On the surface of the Sun, the temperature is 20 times higher than on Earth, at about 6, kelvins, and the centre of the Sun is at about 20 million kelvins. Air becomes liquid around 80 kelvins, a temperature four times lower than the ambient temperature. On our logarithmic scale, the heart of the Sun, five notches above our immediate environment, is ultimately closer to us than optical molasses, eight notches below!
Logarithmic scale of temperatures. Cold atomic gases correspond to the lowest kinetic temperatures ever measured. The combination of the Sisyphus effects due to these waves allows for the movement of the atoms to be frozen in the three directions of space.
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When the atoms penetrate this area, they are literally caught by the light and accumulate in large numbers, making it possible to visualize them. Image of a sodium optical molasses containing a few million sodium atoms at the intersection of three pairs of laser beams. Photography: W. Phillips, NIST, These clocks are our guardians of time and are therefore of great importance, both for industry and services, and for fundamental research.
The reference for time has long been astronomical, founded of the sidereal day. In , during the thirteenth General Conference on Weights and Measures, it was decided to switch to an atomic reference, which, at the time, was considered infallible. Let us once more draw on the fact that, if its colour is well chosen, radiation can induce a transition between the atomic states.
We define the second by positing that the electromagnetic wave capable of inducing optimally the transition between State 1 and State 2 performs 9,,, oscillations per second. A feedback loop locks in the frequency of the electromagnetic wave to maximize this number. As an illustration, we can say that the atoms here play the role of the pendulum, and the electromagnetic wave the role of the counting system.
Block diagram of an atomic clock. I will mention just one, linked to the Doppler effect, which indicates that the wave emitted by a moving source does not have the same frequency as a wave emitted by a stationary one. On the other hand, if the atoms are very slow, the Doppler effect is much weaker and its detrimental role becomes negligible.
If it had functioned since the Big Bang, it would be only a few seconds slow or fast. Its many applications include navigation, satellite navigation, geodesy and, in the near future, very high-speed telecommunication. Certainly not: several paths are currently being explored to render the measurement of time considerably more precise, that is, by a factor of 10 or even