Atomic Radio - the first ever musical show was made

Physicists from the United States created an atomic radio installation in the laboratory, in which Rydberg atoms using two pairs of lasers are used instead of antennas, and conducted the world's first experimental transmission of a stereophonic musical composition using AM radio waves.

Brief description of the experiment

Five years ago, it was proved that sensitive electromagnetic radiation receivers can be made on the basis of Rydberg atoms.

Rydberg atoms are excited atoms, the external electrons of which are at extremely high energy levels, and in such a state these atoms very sharply react to weak changes in the external electric field.
')
In 2019, a more complex experiment was successfully carried out, for which a special laboratory setup was created in the form of a tank with a gas of Rydberg atoms, which is illuminated by two laser sources with different wavelengths.

When radio waves were passed through the capacitance, the absorption spectrum of Rydberg atoms began to shift, and these changes were recorded using lasers. Thus, the installation worked as a receiver of AM radio waves of a certain frequency.

The components of the facility were cesium-133 and rubidium-87 atoms.

The quality of the signal received using such a setup turned out to be quite good in such an experiment.

A more detailed description of the experiment

As described earlier, the Rydberg atom is a highly excited atom whose outer electron has risen to a very high energy level.

As a rule, the main quantum number of this level is n ~ 100.

The properties of the Rydberg atom strongly depend on the number n:

• the lifetime of an atom grows rapidly with increasing n and in proportion to n ^ 3;
• the dipole moment grows as n ^ 2;
• polarizability increases as n ^ 7.

Thus, the stronger the Rydberg atom is excited, the longer it lives and the more acutely the external electric field is felt.

In addition, along with the number n increase:

• the radius of an individual atom (R ~ n ^ 6);
• the characteristic length of the interaction of two atoms (L ~ n ^ 4).

For example , the radius of a hydrogen atom with n = 1000 is approximately 5x10 ^ (- 2) mm, and its lifetime reaches one second.

Theoretically, such properties make it possible to turn Rydberg atoms into sensitive receivers of electromagnetic waves.

Indeed, due to the large dipole moment, such atoms should feel very well the weak changes in the electric field that accompany the electromagnetic wave.

Therefore, if you constantly monitor the state of the atom, for example, highlighting it with a laser, you can restore the amplitude of the wave and the signal that it carries.

Theory is theory, but experiments are needed.

For the first time the idea of ​​creating such a facility (the first version of a completely simplified atomic radio) was proposed in 2014, at the same time the first experiment was successfully carried out by a group of physicists under the leadership of Christopher Holloway, proving the theoretical calculations in reality.



→ Link to article

The scheme of the experiment:



Installation Scheme:



Simulation of the amplitude of the electric field:



Comparison of calculated and obtained data:





After this first experiment, refinements of the experimental setup began to improve its parameters and expand its capabilities — to obtain additional data, for example, the possibility of measuring the phase of a radio wave incident on an atomic gas was realized.

→ Link to article



The scheme of the experiment:





The data obtained:









And now, after the main elements of the atomic radio were opened, it now remains to assemble a more complex and working installation, with which you can listen to music and radio programs.

And the new installation added support for stereo sound, different channels of which are transferred by AM radio waves with different carrier frequencies.

→ Link to full article on this experiment



Scheme of the new installation:



The basis of the new experimental setup is a cavity filled with Rydberg atoms and illuminated by two lasers with different wavelengths.

One of the lasers ("binding") ensures the coherence of the atoms of the receiver, and the second laser ("probing") extracts information from it.

Thanks to the correct setting of the “binding” laser at rest, the atoms of the receiver are transparent to the “probing” laser.

In this case, transparency is achieved only in a narrow frequency range, so the “probe” laser must be very clean. If a radio wave passes through the receiver, the absorption spectrum of the atoms shifts, and the laser radiation begins to be absorbed.

The greater the amplitude of the wave, the stronger the loss. Therefore, such a cavity works as a receiver, which receives AM radio waves with a certain carrier frequency.

In order to achieve the effect of stereo sound, in the experiment they filled the cavity with two types of Rydberg atoms at once, each of which worked independently with its own “binding” and “probing” laser.

Cesium-133 and rubidium-87 were chosen as such atoms, which took waves with a carrier frequency of 19.623 GHz and 20.644 GHz.

The signals from the “probing” lasers were fed to a computer and processed using the free program Audacity.

To test the operation of the atomic stereo AM radio, an improvised melody was transmitted to it in A minor, which was performed on two guitars (electric and acoustic with a pickup).

The signals taken from the guitars were sent to amplifiers, converted to amplitude-modulated form using signal generators, and transmitted using two horn antennas.

The acoustic guitar signal was broadcast at a frequency of 19.623 GHz, and the signal of an electric guitar at a frequency of 20.644 GHz.

Both horn antennas were located at a distance of about 15 centimeters from the cavity filled with Rydberg atoms.

Received signal:





The quality of the recovered signal turned out to be quite acceptable: in spite of small interferences, resembling the crackle of a vinyl record, the music was very clear.

Record the received signal posted in open access here .

→ Listen to it online here.



Thus, in their new work on music, physicists were able to show that quantum physics can be not only complicated, but also interesting.