Quantum Clocks Sense Gravitational Time Dilation ⚡ экспресс
Gravitational time dilation causes the proper times of clocks at different altitudes to differ. A quantum interferometer is considered with photonic clocks based on frequency combs, stored in two vertically separated quantum memories, so that the joint state evolves in a superposition of two proper times. After retrieval from memory, the photons interfere in a Hong–Ou–Mandel scheme, for which analytical expressions for multi-photon counting statistics are obtained. When transitioning from pairs of entangled photons to 2N-photon frequency-entangled states, the proper-time-dependent phase is amplified N-fold, accelerating the collapse and revival of the interference signal. Accounting for finite efficiency and memory lifetime, regimes where the modulation remains observable are identified. For parameters compatible with existing rubidium and cesium memories, the first collapse occurs at height differences on the order of 10–100 m and storage times from fractions of a second to several seconds, and combinations with rare-earth ions and alkali elements allow the required height to be reduced to a few meters.
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. The particles are sent into two light traps at different heights, where they wait while time diverges for them. Then they're released and blended in a Hong–Ou–Mandel device. If the photons are in sync, they cancel each other out, and the detector stays silent—like two tuning forks in unison. But gravity shifts the light's frequency (color), breaking the harmony. To amplify the effect, instead of a pair, they use an ensemble of many particles. Then even the slightest off-key note is more noticeable—a choir is louder than a soloist.
This approach brings the test of quantum physics in curved spacetime right into the lab.
🎯 Over a year, the clock-time difference between a basement and an attic is less than a billionth of a second—the new method makes it noticeable in just a couple of seconds.
🎬 In the movie "Interstellar," time slows dramatically near a black hole; here, it's a modest but real laboratory echo.