Disclosure of Invention
In order to solve the technical problem, the invention provides a method for generating a low-light low-speed stable light soliton.
The technical scheme adopted by the invention is as follows: a method for generating low-speed stable optical solitons of weak light by optically detecting the incoherent pumping light gamma of field gain21The method is applied to an inverted Y-shaped four-energy-level Reedberg cold atom system with a prolonged service life, the interference between atom quantum states induced by control light with larger light intensity is utilized to eliminate the absorption of a resonant medium on incident light with weaker light intensity, a larger nonlinear effect is obtained, and a stable light soliton with space-time (PT) symmetry is obtained.
The four-energy-level inverted Y-shaped rydberg cold atom system with the widened service life has the energy levels of atoms of |1>=|5S1/2,F=1>,|2>=|5S1/2,F=2>,|3>=|5P3/2,F=3>And |4>=|60S1/2>Wherein 5 and 60 represent the number of principal quantums, S1/2Denotes the S orbit with a spin quantum number of 1/2, F denotes the total angular momentum, P3/2Represents the P orbit with a spin quantum number of 3/2. A bundle of pull ratio frequency of A S-1Weak detection light field omegapAnd a bundle of pull ratio frequencies of B S-1Strongly controlled light field omegacCoupled respectively to |1>→|3>And |2>→|3>A bundle of pull ratio frequencies of C S-1Auxiliary light field omegaaCoupling |3>→|4>Their field distribution functional relationship Ep≤Ea<<Ec(ii) a Wherein A, B, C is a preset value.
The specific implementation comprises the following substeps:
step 1: the method comprises the following steps of trapping a Reidberg atomic gas in a magneto-optical trap, wherein the ambient temperature of the atomic gas is in the order of nanometer Kelvin, and the Doppler effect caused by the mass center movement and the thermal movement of atoms is negligible;
step 2: will have a ratio frequency of B S-1The control light field of the spatial modulation is incident into the gas according to a preset direction, and the frequency coupling energy level is |3>→|4>A transition of (c);
and step 3: will have a pull ratio frequency of A S-1Detected light field omegapSum-to-ratio frequency of C S-1Auxiliary light field omegaaAfter focusing and collimating, the light beam reversely propagates in the gas;
and 4, step 4: locking the frequency of the detection light field on a transition line of a rydberg atomic gas atomic energy level |1> → |3>, controlling the frequency of the light field to be adjusted to be close to the transition line of the rydberg atomic gas atomic energy level |2> → |3>, applying DHz to the detection light field, and modulating FHz to the modulation amplitude; wherein D, F is a preset value;
and 5: in the whole process, the optical power is kept and controlled to be unchanged, the frequency of the detection light is scanned near a transition line of atomic energy level |1> → |3> of the atomic gas of the Reedberg, the transmission light intensity and the phase of the detection light after passing through the atomic gas are detected, and then demodulation is carried out to obtain the stable optical soliton.
Theoretical and experimental studies show that the cold atoms in the rydberg can establish an optical nonlinear system with strong and long optical path. By introducing Electromagnetic Induction Transparency (EIT) of the gas of the cold atoms in the Reidberg, the absorption of the resonant medium to the incident light with weaker light intensity is eliminated by the interference between the atomic quantum states induced by the control light with larger light intensity through the interaction of the light and the cold atoms, and a larger nonlinear effect is obtained to obtain the stable optical solitons. Different from the classical nonlinear material method, the optical soliton obtained by the invention not only has space-time (PT) symmetry, but also supports low speed (the group velocity is hundreds of meters per second) of non-local weak light (nano watt level), so that the optical soliton with the characteristic can be more concerned and applied.
Compared with the prior art, the invention has the beneficial effects that:
(1) the invention provides a method for generating stable LBs based on a Reedberg cold atom decorated EIT. The method obtains stable LBs (ground state optical solitons, dipolar optical solitons, quadrupole solitons and vortex optical solitons) and dynamic characteristics thereof by regulating and controlling a real part and an imaginary part of PT symmetrical potential and Kerr non-local nonlinear coefficients. Analysis shows that the optical solitons not only have an ultra-slow propagation speed, but also have extremely low generated power.
(2) The method provided by the invention opens up a development approach of non-Hermite nonlinear optics, and particularly utilizes controllable PT symmetrical optical potential and non-local Kerr nonlinear manipulation LBs to realize stable PT symmetrical optical solitons with non-local weak light and low speed characteristics, so that the stable PT symmetrical optical solitons can be widely applied to the technical fields of optical communication and optical transmission.
(3) The method provided by the invention is simple and easy to understand, convenient to realize and strong in practicability, can be used for adjusting related parameters according to actual conditions, and provides powerful support for deep application and development of the optical solitons in the technical field of optical communication.
Detailed Description
In order to facilitate the understanding and implementation of the present invention for those of ordinary skill in the art, the present invention is further described in detail with reference to the accompanying drawings and examples, it is to be understood that the embodiments described herein are merely illustrative and explanatory of the present invention and are not restrictive thereof.
For convenience of explaining the method for generating the low-speed stable light solitons with weak light, the four-energy-level inverted-Y-shaped rydberg cold atom system with a widened lifetime is introduced in the embodiment as shown in FIG. 1, and the embodiment selects88Sr is selected as the four-level inverted Y-shaped Reedberg cold atom system with the lifetime widened88Sr atomThe four energy levels of the son are respectively |1>=|5S1/2,F=1>,|2>=|5S1/2,F=2>,|3>=|5P3/2,F=3>And |4>=|60S1/2>. A bundle of pull ratio frequency of A S-1Weak detection light field omegapAnd a bundle of pull ratio frequencies of B S-1Strongly controlled light field omegacCoupled respectively to |1>→|3>And |2>→|3>A bundle of pull ratio frequencies of C S-1Auxiliary light field omegaaCoupling |3>→|4>Their field distribution functional relationship Ep≤Ea<<Ec(ii) a The quantum effect of the optical field is not significant and can be handled as a classical electromagnetic field. Another incoherent pump light (gamma)21) For this system, the control field and the auxiliary field are spatially modulated. Delta3For single-photon detuning, Δ2And Δ4For two-photon detuning, the decorated Reidberg EIT scheme (Δ)3+Δ4>>Ωa). This example studies that the density of the gas at the rydberg atoms is small and the local non-linearity caused by the interaction between light and atoms cannot be neglected.
The specific implementation of the embodiment comprises the following steps:
step 1: a gas of a Reedberg atom (88Sr) is confined in a Magneto-optical trap (MOT), the ambient temperature of atomic gas is in the order of nano Kelvin, and the Doppler effect caused by the mass center movement and the thermal movement of atoms is negligible;
step 2: will have a pull ratio frequency of B S-1Of the spatial modulation of (2) the control light field omegacIncident into the gas in a predetermined direction, and frequency-coupled to an energy level |3>→|4>A transition of (c);
and step 3: will have a pull ratio frequency of A S-1Detected light field omegapSum-to-ratio frequency of C S-1Auxiliary light field omegaaAfter focusing and collimating, the light beam reversely propagates in the gas;
and 4, step 4: locking the frequency of the detection light field on a transition line of a rydberg atomic gas atomic energy level |1> → |3>, controlling the frequency of the light field to be adjusted to be close to the transition line of the rydberg atomic gas atomic energy level |2> → |3>, and applying shallow amplitude frequency modulation with the modulation frequency of DHz and the modulation amplitude of FHz to the detection light field;
and 5: in the whole process, the optical power is kept and controlled to be unchanged, the frequency of the detection light is scanned near a transition line of atomic energy level |1> → |3> of the atomic gas of the Reedberg, the transmission light intensity and the phase of the detection light after passing through the atomic gas are detected, and then demodulation is carried out to obtain the stable optical soliton.
The weak detection light field omega of the present embodimentpHas a value range of 106<A<3×106Strong control of light field omegacHas a value range of 107<B<3×107Auxiliary light field omegaaThe range of the value of the draw ratio frequency is 5 multiplied by 106<C<1.5×107The modulation frequency has a value range of 103<D<104The value range of the modulation amplitude is 107<F<108。
Fig. 2 is a schematic diagram of an experimental scheme corresponding to this embodiment and a schematic diagram of propagation directions of respective optical fields. The whole big sphere is a mode-locked super atom, the dotted circular inner sphere is a Reidberg atom, omegap、ΩaAnd omegacIn parallel in opposite directions in the gas of the rydberg atoms.
A schematic representation of the blockage effect of the reed castle is shown in fig. 2. The excitation of atoms within the occluding sphere is hindered by long range interactions between the rydberg atoms, the boundaries of which are represented by the dashed circles in this embodiment. Only one atom (the hollow sphere in the center of the dotted circle) in each occluding sphere is excited to the rydberg state, and the remaining atoms (the hollow spheres in the dotted circle) cannot be excited to the rydberg state due to the occluding effect. The kinetics of the light-rydberg atom interaction system is described in terms of hamiltonian under the heisenberg representation:
is the system Hamiltonian, N
aIs the atomic gas density, r represents the distance between the rydberg atoms,
is the Hamiltonian of the r atom position, d
3r represents the triple integral over space and t represents time.
Under the approximation of electric dipoles and spin waves, the main equation of the system density matrix evolution is as follows:
wherein
Being a density matrix, Γ is a relaxation matrix, which describes atomic state spontaneous emission and atomic system decoherence; i represents an imaginary unit,
Representing the planck constant.
Under paraxial and slowly varying envelope approximations, the maxwell's equations for probe light are:
wherein omegapFor detecting the optical contrast ratio frequency, c is the speed of light, omegapTo detect the optical frequency, z, x, y represent three dimensional coordinates in space.
For detecting the optical polarizability, wherein
(1)Linear polarizability, which is a symmetric potential with respect to PT,
and
for local and non-local third-order nonlinear polarizabilities,
and
for local and non-local fifth order nonlinear polarizabilities,
and
depending on the interaction between the light and the atoms,
and
then depends on the interaction between the rydberg atoms, such as the interaction potential V (r-r') between the rydberg atoms and the atomic gas density N
aAnd the like.
The dimensionless nonlinear equation of the detection field pulse satisfies:
wherein psi ═ omega
p/ψ
0To detect the typical rabi frequency of the field pulses, s-z/(2L)
diff),r
⊥=(x,y,0),(ξ,η)=(x,y)/R
⊥Coefficient of dispersion
Wherein
R
⊥Typical radius of curvature of the probe field pulse. gamma-2W
1|ψ
0|
2L
diffIs in photo-atomic phaseThe nonlinear coefficients of the local Kerr effect of the interaction contributions,
the system non-local scale coefficient is represented, pi is PT symmetrical potential, and V is long-range interaction potential between rydberg atoms.
A step fourier method can be used to solve the stable digital solution of equation (4). In the present invention, the present embodiment adopts88Sr as the inverted "Y" type four-level atomic system in fig. 1, the parameters involved in the proposed method are chosen as follows: r⊥=12μm,τ0=1.1×10-6s,τ21=0.2πMHz,Γ3=2π×106MHz,Γ4=Γ34=2π×16.7kHz,Δ2=1.67×106s-1,Δ3=9.67×107s-1,Δ4=1.36×107s-1,Na=1.0×1012cm-3,Ωc=1.5×107s-1,Ωa=1.0×107s-1,V0=21.17。
Fig. 3 is a characteristic diagram of the ground state optical soliton (a) and the dipolar optical soliton (d) realized by the method provided by the invention. The (a1, d1) is a cross section, (a2, d2) is a field mode diagram, and (a3, d3) is a phase diagram. Therefore, the method provided by the invention can generate stable PT symmetrical optical solitons and realize the stable transmission of the ultra-low-speed low-power optical solitons.
The method provided by the invention has the advantages that: the invention provides a Reedberg cold atom decoration state EIT method based stable PT symmetrical optical solitons, which solves the problem that the stable optical solitons are difficult to generate in the technical field of optical communication, and the realized PT symmetrical optical solitons have the characteristics of ultra-low speed and low power. The optical soliton realized by the invention has wide application prospect in the technical field of optical communication.
It should be understood that the above description of the preferred embodiments is given for clarity and not for any purpose of limitation, and that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims.