Passing on Experience
The Michelson Interferometer uses the amplitude division method to generate two beams to achieve interference, and it holds a certain position in Modern Physics.
Shen Qi is conducting this experiment, which is one of several fundamental physics experiments.
The beam expander was moved outside the Michelson optical path, the Helium-Neon Laser support was adjusted, and the beam was aligned with the target to make the beam parallel to the instrument's stage. The distance from the incident and exit points of each optical mirror to the stage was controlled to be approximately 70mm... Shen Qi strictly followed the experimental procedure. This basic optical experiment in Modern Physics was not difficult; what it tested was patience and meticulousness.
After recording the raw data, Shen Qi quickly calculated the laser wavelength and air refractive index, and handed the manuscript to an experimental teaching assistant in the Department of Physics.
The young teaching assistant checked Shen Qi's record sheet and nodded. "OK, no problem."
"Senior, are you also in charge of the comprehensive design experiment?" Shen Qi asked.
"Yes, Teacher Ren has already explained it." The experimental teaching assistant seemed to respect Professor Ren a lot; he was an outstanding graduate student in the School of Physics.
"What about conducting innovative experiments?" Shen Qi asked again.
The teaching assistant chuckled, "I'll take care of it. In short, for anything related to undergraduate experiments, just come to me."
"Thanks, brother. By the way, what's your name?" Shen Qi thought to himself that Grandpa Ren was quite influential, getting my physics experiment arrangements sorted out in no time.
"My name is Qin Hao, and I'm a second-year graduate student," the lab teaching assistant said, then humbly asked, "Shen Qi, I have a question for you. How exactly does the Princeton interview process work?"
"It's very simple. Just chat with the foreign interviewer. The interview usually lasts about an hour, with 45 minutes in English and 15 minutes in Chinese."
"These foreigners are really impressive these days; they speak Chinese incredibly fluently," Shen Qi said, sharing his experience.
"Just empty talk? Doesn't the interviewer ask any academic questions?" Qin Hao asked again.
"Brother Hao, I don't know how others conduct their interviews, I can only share my own experience."
"The American interviewer started by praising me, saying my paper data was excellent, and then asked me, 'Hey, Shen, do you have any interesting or special experiences?'"
"I didn't have any particularly exciting or special experiences, so I just reminisced about my past, from high school all the way to my sophomore year of college, and then a few days later, I received an offer from Princeton."
Shen Qi patiently explained as many interview details as possible to Qin Hao, emphasizing the importance of mutual assistance, as they would need Qin Hao's coordination for the next two physics experiments. "So, Brother Hao, you also want to go to Princeton?"
"I have this idea; I want to pursue a PhD at Ivy League school."
"But Princeton is too difficult to get into, so maybe my goal should be University of Pennsylvania or Cornell."
Qin Hao said with great envy, "Shen Qi, you're amazing! You got an offer from Princeton in your sophomore year, an offer from the Princeton Mathematics Department."
Shen Qi said, "The interview process for Ivy League schools is probably similar; it mainly assesses the applicant's oral communication skills."
"When communicating with the interviewer, avoid being incoherent, rambling, or having a confused logic. The topic of conversation isn't the key; the key is to be confident and composed during the conversation. This is just my personal opinion, for your reference only." At this moment, Shen Qi seemed more like an experienced senior.
"Thank you for sharing!" Qin Hao said gratefully. He understood the written application process for Ivy League schools, but he didn't know if the information online about interviews was true or false.
The most reliable source of advice is, of course Shen Qi, who just finished his Princeton interview and passed it successfully.
Under Professor Ren's arrangement and Qin Hao's specific coordination, Shen Qi participated in the Physics Department's comprehensive design experiment the following day.
Similarly, for an optical experiment, Shen Qi gave it a nice name, "Telepathy Between Photons," and listed the necessary experimental instruments.
Unlike basic experiments with standardized, fixed procedures, comprehensive design experiments require the experimenter to design their own scheme.
The experimental equipment that Shen Qi applied for was very simple: a light source emitter, two detectors, several ordinary lenses, and one semi-transparent lens.
Under Qin Hao's supervision, Shen Qi began the "Telepathy Between Photons" experiment.
Shen Qi carefully adjusted the light source emitter, continuously reducing the power of the incident light until it emitted an extremely faint light, which he then passed through the translucent mirror.
A semi-transparent mirror is a special type of mirror that allows light to pass through on one half while reflecting it on the other.
The incident light is split into two segments by a semi-transparent lens, and then their paths are changed by ordinary lenses before finally reaching the photon detector.
At this stage of the experiment, we've entered the realm of Quantum Mechanics, and the question to be solved is: what exactly is light?
Newton believed that light was composed of tiny particles invisible to the human eye, while Huygens, a contemporary of Newton, believed that light was a wave.
The two leaders and their respective followers have been arguing for over a hundred years without a clear winner.
It wasn't until Thomas Young conducted his famous double-slit experiment that decisive evidence was obtained that light is a wave.
However, the debate continued, and soon Einstein stepped forward, siding with Newton and arguing that Light Quantum Hypothesis was born, ushering in a new era in physics.
Now everyone knows that light has Wave-Particle Duality.
Wave-like and particle-like properties are two extremely opposing characteristics, like two sides of a coin. We can only ever see one side, but we cannot deny the existence of the other side.
The emergence of wave and particle properties in photons is as random as flipping a coin; the outcome is 50/50, completely random. In physics, this is called Quantum Entanglement, which is the theoretical basis for quantum cryptography.
Quantum cryptography is far more advanced than the Vigenère Cipher used for flirting. The elective course "Cryptography" in the Mathematics Department only briefly mentions it, and Shen Qi's understanding of it is relatively superficial. This is a very application-oriented field.
Shen Qi operated the experimental equipment, using two different detectors to receive photons.
Photons received by a wave detector exhibit wave-like properties, while photons received by a particle detector exhibit particle-like properties.
In fact, these photons originate from the same weak light source. After being split by the half-lens, the wave-particle duality depends on the properties of the detector.
Having completed the experiment to this point, Shen Qi could call it a day. He replicated Wheeler's "delayed selection experiment," thoroughly proving the Wave-Particle Duality of light.
Whether it was Einstein or Bohr, the leading figures in Quantum Physics at the beginning of the 20th century proposed directions and insights in theory, but due to the limitations of experimental conditions at the time, they could not perfectly prove them with experimental data. Even the most basic Quantum Physics experimental instruments of the 21st century were like divine tools in Einstein's time.
Shen Qi prefers to believe that photons possess twin properties, and that his experiment is not over; he continues his experiments using twin photons.
Twin photons are two photons that vibrate in the same direction, as if they were exchanging instantaneous information with other photons at a distance through "telepathy".
"Brother Hao, my integrated design experiment is finished. This is the best I can do. Research on High-Speed Quantum Computer is beyond my capabilities." Shen Qi shut down the experimental equipment, signed the record sheet, and handed it to Qin Hao.
"That's beyond my capabilities." Qin Hao took Shen Qi's experimental record sheet, signed it, and then he would report it to the physics department teacher and write a preliminary evaluation for Shen Qi as an experimental teaching assistant.
Shen Qi completed two physics experiments in two days, and there is one last innovative research experiment left, which requires some preparation time.