quantum clock interference

Ordinary atomic clocks are like a tuning fork that must be kept in perfect silence and stillness. The slightest movement, and the note goes flat. The same goes for atoms: their thermal motion shifts the frequency of radiation, so ultra-precise clocks require almost complete immobilization of the particles.

Light loves symmetry: in an open channel, it flows equally both ways. To steer it one way, physicists often use magnets. A new approach does without, using rotation — just the speed of a vinyl record — and interference from two atoms. Rotation changes the “pitch” of light for different directions, just as a siren’s tone shifts when a car approaches or recedes.

A clock isn't just hands. Every atomic nucleus is a natural metronome: it oscillates with nearly perfect regularity. If you lift one such metronome a couple of meters, its rhythm speeds up ever so slightly — that's time warping, as predicted by Einstein.

In the headphones used to listen to a distant orchestra, there is an occasional crackle. The crackle can be so loud that it drowns out the music or even blends in with it.

A laser beam hits an atom, and an electron is knocked loose. It accelerates, returns, and, crashing into the atom, emits a flash of light — a harmonic. If there are two light beams and they are crossed like an intersection, the electron can choose different routes. In the new experiment, the two beams had comparable strength and were directed at right angles.

Light in an optical fiber is a stream of photons, and quantum communication requires single photons that can be sent one at a time. But making them emerge quickly while remaining indistinguishable from one another is a tough challenge.

Two clocks in different rooms need to tick in unison. Usually, this is done by sending bright pulses or pairs of photons that arrive one right after the other. But the signal can be so weak that photons barely make it through. In this work, clocks were synchronized with light a billion times dimmer than usual.

Inside a tiny mirrored cavity, smaller than the thickness of a hair, light is trapped and bounces off the walls many times. If you place a material that can absorb and emit light inside, the light particles (photons) start to 'dress' in excitations of the material — this is how polariton modes are born.

Time flows slower near the ground than on the roof: this was predicted by Einstein in his theory of relativity. To spot the tiny difference, physicists propose using a pair of photons, linked like voices in a duet.

A ruler made of light: that's one way to describe a new method for measuring tiny time delays. In 1987, Chong Ki Hong, Zhe-Yu Ou, and Leonard Mandel noticed that when two indistinguishable photons hit a beam splitter simultaneously, they always exit together from the same port.