Have Two Photons Ever Been Observed Landing on the Exact Same Spot?

That's a fascinating question! Given the huge number of photons involved in forming interference patterns or images, it seems natural to ask whether two photons have ever been observed landing on the exact same spot.

1. Theoretical Possibility: Can It Happen?

Mathematically, yes, two photons can land on the exact same spot, since:

• The wavefunction’s probability distribution allows for any point on the screen to be hit by a photon.
• Photons are bosons (they can “bunch” together, unlike electrons).
• The sheer number of photons in practical experiments makes this more likely to occur at high-intensity photon counts.

However, since probability distributions are continuous, the odds of any specific spot being hit twice in a short period are extremely small for individual photons.

2. Experimental Reality: Can We Detect This?

In practical experiments, whether two photons land in the "same spot" depends on how "spot" is defined:

• Modern detectors (CCDs, photomultipliers, etc.) have pixel sizes ranging from micrometers (µm) to nanometers (nm).
• Two photons hitting the same pixel (which is not exactly the same atomic-scale location, but close enough) is very common.
• However, detecting two photons hitting exactly the same quantum state (i.e., landing in the same location at the same time) is much harder.

Some advanced quantum optics experiments have observed photon bunching, where multiple photons tend to arrive at the same detector pixel more often than expected.

3. Has It Ever Been Observed?

Yes, but with specific experimental conditions:

• In low-intensity, single-photon double-slit experiments, photons arrive one at a time, making it hard to observe two at the same place at once.
• In high-intensity laser experiments, multiple photons hit the same detector pixel all the time.
• Photon bunching (two photons arriving at the same detector) has been directly observed in quantum optics experiments like the Hong-Ou-Mandel (HOM) effect, where two photons interfere and tend to arrive at the same location more often than chance alone would predict.

Example:

The Hong-Ou-Mandel effect is a well-known experiment where two identical photons are sent into a beam splitter. Instead of going separate ways, they both exit the same port, meaning they land in the same detector at the same time. This shows that photons can exhibit bunching behavior.

4. What About in an Everyday Photo?

If you’re talking about a photo made of billions of photons (like on a digital camera sensor):

• Yes, many photons hit the same pixel! This is normal in everyday imaging.
• However, the quantum mechanical question is stricter: Have two photons hit the exact same microscopic location at exactly the same time?
  • This is difficult to measure because most detectors cannot resolve individual photon impacts with atomic precision.
  • Instead, they sum photon arrivals over time (integrating the light into an exposure).

5. Final Answer:

• Yes, photons landing on the same pixel in a detector has been observed.
• Yes, photon bunching (two photons hitting the same detector simultaneously) has been experimentally verified in quantum optics.
• However, observing two photons landing on the “exact same spot” at the atomic level in a real-world setting is nearly impossible with current technology.
• In everyday photography, billions of photons naturally hit the same pixels, but individual quantum coincidences are hard to measure.

🚀 Would you like me to dive deeper into photon detection limits or specific experiments that study photon clustering?

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