The wave function of a single photon is usually a 'wave packet'. But in theory, as long as the photon is not directly detected, its wave function can be manipulated to any complex shape. Scientists have been able to filter single photons in the near future, thus narrowing the frequency range of wave packets. But changing the time dependence of photon wave packets is even more difficult, and it is necessary to know when the photon is presentmodulatorIn the process, it will take time to change it. The typical packet duration of a pair of entangled photons is only one tenth of a picosecond, which is too short for existing technology.

Now the situation has changed. Scientists at Stanford University in the United States have generated entangled photon wave packets with a duration of nearly one microsecond. They use existing technologies called "slow light" or "electromagnetic induction transparency" to perform singlePhoton modulationFirstly, they generated a pair of photons with slightly different frequencies in rubidium gas. Photons with low frequencies travel in gas at speeds close to traditional light, while photons with high frequencies move at approximately 1/10000 the speed of light due to their interaction with rubidium. Inelectro-optic modulatorIn China, the detection of fast-moving photons indicates the arrival time of slow-moving photons. Because it is impossible to directly measure the wave packet, scientists have detected a large number of identical photons and plotted the probability of photons appearing on the detector every 300 nanoseconds. In these figures, they represent a single photon wave packet shaped into two 50 nanosecond long square pulses. They also generated Gaussian and exponential wave packets. In the past, in order to obtain special wave packet shapes, single photons had to be generated in special containers. but nowelectro-optic modulatorProvides a higher degree of control. This work is of great importance in both fundamental and practical aspects, and can be applied to quantum cryptography as well as quantum computer memory.