Michelson interferometers use the partial amplitude method to generate two beams to achieve interference, which has a certain place in modern physics.

Shen Qi is doing this experiment, which is one of several basic physics experiments.

Transfer the beam expander to the outside of the Michelson optical path, adjust the HeNe laser bracket, cooperate with the light target to make the beam parallel to the table of the instrument, and control the distance from the incident and exit points of each optical mirror to the table surface is about 70mm...... Shen Qi strictly follows the experimental operation process, this optical basic experiment of modern physics is not difficult, and the test is patience and carefulness.

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 at the Institute of Physics.

The young experimental assistant checked Shen Qi's record paper and nodded, "OK, there's no problem." ”

"Senior brother, you are also in charge of comprehensive design experiments?" asked Shen Qi.

"That's right, Teacher Ren has already explained. "The experimental teaching assistant seems to have a lot of respect for Professor Ren, who is an excellent graduate student in the School of Physics.

"What about researching innovative experiments?" Shen Qi asked again.

The experimental teaching assistant smiled: "I'm still in charge, all in all, you can find me in terms of undergraduate experiments." ”

"Thank you, brother, by the way, what do you call my brother?" Shen Qixin said that Old Man Ren is quite energetic, and he can arrange my physics experiment in minutes.

"My name is Qin Hao, and I am currently in my second year of graduate school. The experimental teaching assistant said, and then asked humbly: "Shen Qi, let me ask you something, how does the interview at Princeton work?"

"It's very simple, just blow water with that foreigner interviewer, the interview time is generally about 1 hour, 45 minutes to speak English, 15 minutes to speak Chinese. ”

"Now these foreigners are very powerful, and they speak super slippery Chinese. Shen Qi said, imparting experience.

"The interviewer doesn't look at academic questions?" Qin Hao asked again.

"Brother Hao, I don't know how others interview, I can only talk about my own interview experience. ”

"The American interviewer started by complimenting me on my excellent numbers on paper, and then asked me, Hey, Shen, did you have any wonderful and special experiences?"

"I didn't have any wonderful and special experiences, so I reminisced about my past, from high school to my sophomore year, and then a few days later, I received an offer from Princeton. ”

Shen Qi patiently told Qin Hao as many details of the interview as possible and helped each other, and the next two physics experiments had to rely on Qin Hao's coordination: "So, Brother Hao also wants to go to Princeton?"

"I had this idea and wanted to go to the Ivy League for a PhD. ”

"But Princeton is too hard to apply to, and maybe I'll be aiming for Penn or Cornell. ”

Qin Hao said very enviously: "It's still Shen Qi, you are a cow, you got an offer from Princeton in your sophomore year, an offer from the Princeton Department of Mathematics." ”

Shen Qi said: "The interview procedures of those Ivy League schools are estimated to be similar, mainly to test the applicant's oral expression ability. ”

"When communicating with the interviewer, you should avoid incoherent language, incoherent preamble, and confusing logic. It's not about what topics to talk about, it's about being confident and calm when communicating. Personal opinion, for informational purposes only. At this time, Shen Qi was more like an experienced senior brother.

"Thank you for sharing!" Qin Hao said gratefully, he understands the written process of applying to Ivy League schools, and he doesn't know whether the information on the Internet is true or false about interviews.

The most reliable consultation channel is, of course, to consult Shen Qi, who has just participated in the Princeton interview and successfully passed.

Under the arrangement of Professor Ren and the specific coordination of Qin Hao, Shen Qi participated in the comprehensive design experiment of the Institute of Physics the next day.

It was also an optical experiment, and Shen Qi gave the experiment a nice name "telepathy between photons" and made a list of the experimental instruments needed.

Different from the basic experiments of modeled fixed program operation, comprehensive design experiments require the experimenter to design the scheme by himself.

The experimental instrument that Shen Qi applied for was very simple, a light source emitter, two detectors, several ordinary lenses, and one and a half lenses.

Under Qin Hao's supervision, Shen Qi began the experiment of "telepathy between photons".

Shen Qi carefully adjusted the light emitter, constantly reducing the power of the incident light until it finally emitted an extremely faint light and let it pass through the half-lens.

A halflens is a special type of mirror where half of the light can pass through and the other half is reflected.

The incident light is divided into two segments by a half-lens, which then changes their path separately with a normal lens until it reaches the photon detector.

At this point in the experiment, we have actually entered the field of quantum mechanics, and the question to be solved is, what is light?

Newton believed that the essence of light was tiny particles that could not be seen by the human eye, while his contemporary, Huygens, believed that the essence of light was a wave.

The two bigwigs and their respective followers have been arguing for more than 100 years without a win.

It wasn't until Thomas Young conducted the famous double-slit experiment that conclusive evidence that light was a wave was obtained.

However, the debate continued, and soon after Einstein stood up with Newton and argued that light has particles, thus giving birth to the quantum theory of light and opening a new era in physics.

Now everyone knows that light has wave-particle duality.

Volatility and particle nature are two polar opposites, like heads and tails of a coin, we can only see one side of the coin, but we can't deny the existence of the other.

When the wave and particle properties of photons appear are like flipping a coin, five or five open, completely random, and the physical term is called quantum correlation, which is the theoretical basis for the setting of quantum cryptography.

The quantum cipher is more high-end than the Virginia cipher used to flirt with the girl, and the elective course "Cryptography" in the Department of Mathematics is only a few simple descriptions, and Shen Qi is shallow, which is a very applied field.

Shen Qi operates the experimental instrument and receives photons through two different detectors.

The photons received by the wave detector are wave-like, and the photons received by the particle detector are particle-like.

In fact, these photons come from the same faint light source, and after being split by the half-lens, the characteristics of the wave particles depend on the properties of the detector.

At this point, Shen Qi can call it a day, and he has copied the "delayed choice experiment" of contemporary physicist Wheeler to thoroughly prove the wave-particle duality of light.

Whether it is Albert Einstein or Bohr, the great masters of quantum physics in the early 20th century put forward directions and insights theoretically, but due to the experimental conditions at that time, they could not be perfectly proved by experimental data. Even the most basic experimental instruments of quantum physics in the 21st century were artifacts in Einstein's time.

Shen Qi prefers to think that photons have twin properties, and his experiment is not over, he uses twin photons to continue the experiment.

Twin photons, i.e., two photons vibrating in the same direction, as if the photons were exchanging instantaneous information with other photons in the distance through "telepathy".

"Brother Hao, my comprehensive design experiment is over, I can only do this step, the research of high-speed quantum computers is beyond my ability. Shen Qi turned off the experimental instrument, signed on the record paper, and handed it to Qin Hao.

"It's also beyond my reach. Qin Hao took Shen Qi's experimental record paper and signed it, after which he would report to the teacher of the Institute of Physics, and write a preliminary comment to Shen Qi as an experimental teaching assistant.

Shen Qi completed two physics experiments in two days, and there was one research innovation experiment left, which required some preparation time.