CN102130418B - Polarization-entangled quantum light source - Google Patents

Abstract

The invention discloses a polarization-entangled quantum light source. The light source includes: a pump light generating device for generating pulsed pump light and inputting it into a third-order nonlinear optical waveguide; a third-order nonlinear optical waveguide with a double Refractive properties, used to independently excite the spontaneous scalar four-wave mixing process on two polarization axes, generate signal and idler two-photons with polarization entanglement properties, and suppress the spontaneous vector four-wave mixing process; optical splitting filter device for The signal output by the third-order nonlinear optical waveguide is separated from the idler frequency photon and the pulse pumping light to obtain polarization-entangled two-photon. The polarization-entangled quantum light source of the invention has a simple and compact structure, and the efficiency of generating and collecting polarization-entangled two-photons is high.

Description

Polarization Entangled Quantum Light Source

technical field

The invention relates to the technical field of quantum information science, in particular to a polarization-entangled quantum light source.

Background technique

Using the basic principles of quantum mechanics, quantum information technology can realize many applications that cannot be realized by classical information technology, which has important academic significance and application value. Quantum entanglement (quantum entanglement) is an important quantum resource on which the realization of quantum information functions depends, and it is a phenomenon of quantum mechanics. It describes by definition a special class of quantum states of composite systems (having more than two subsystems). This quantum state cannot be decomposed into the tensor product (tensor product) of the respective quantum states of the subsystems, which is a non-local correlation between physically separated subsystems. For multiple subsystems in quantum entanglement, the measurement result of any subsystem cannot be independent of the state of other subsystems. Quantum systems that realize quantum entanglement are diverse, such as atoms, ions, and photons. Among them, due to the characteristics of photons that are easy to transmit and not easy to interact with the environment to cause decoherence, entangled two-photons become the most convenient entangled quantum system in quantum information technology. Common two-photon entanglement forms include: momentum and position, time and energy, time slice, polarization state, frequency, and orthogonal amplitude and phase information of the light field. In quantum information technology applications, polarization-entangled two-photons are widely used because the polarization state of photons is easy to control and switch. Therefore, the polarization-entangled quantum light source that produces polarization-entangled two-photons has become a key functional unit in quantum information technology.

Polarization-entangled quantum light sources can be realized by utilizing spontaneous nonlinear optical processes in nonlinear optical materials. At present, the method commonly used in the laboratory is to use the second-order nonlinear parametric down-conversion process in the crystal to realize the generation of polarization-entangled two-photons. On the one hand, this method relies on bulk optics and requires precise optical collimation and adjustment; on the other hand, it is difficult to efficiently collect photons generated from crystals into optical fibers. These all limit the practical development of crystal-based polarization-entangled quantum light sources.

Contents of the invention

(1) Technical issues

A technical problem to be solved by the present invention is: how to provide a simple and compact polarization-entangled quantum light source to improve the efficiency of polarization-entangled two-photon generation and collection.

(2) Technical solutions

In order to solve the above problems, the present invention provides a polarization-entangled quantum light source, which includes: a pump light generating device for generating pulsed pump light and inputting it into a third-order nonlinear optical waveguide; a third-order nonlinear optical waveguide The optical waveguide, which is divided into two sections equally and welded with a 90-degree offset of the polarization axis, has birefringence properties and is used to independently excite the spontaneous scalar four-wave mixing process on the two polarization axes to generate polarization entanglement properties. Signal and idler two-photon, and suppress the spontaneous vector four-wave mixing process; optical splitting filter device, used to separate the signal photon, idler photon and pulse pump light output by the third-order nonlinear optical waveguide to obtain polarization entanglement two-photon;

The pump light generating device further includes: a pulse light source, used to output pulse pump light, by adjusting the polarization state of the pump light to make the power levels of the pump light components on the polarization axes of the two optical fibers consistent, and along the polarization axis direction of the two optical fibers The intensity of the excited two spontaneous scalar four-wave mixing processes is equal, and the independently generated signal and idler two-photon states overlap in time and space; the pump filter is connected to the output of the pulsed light source, and is used to convert the pulsed The stray light other than the wavelength of the pulse pump light output by the light source is filtered; the adjustable attenuator is used to adjust the power of the pulse pump light output by the pump light filter; the polarizer is used to adjust the adjustable The polarization state of the pulse pump light adjusted by the attenuator is converted into linear polarization; the polarization controller is used to adjust the polarization state of the pulse pump light adjusted by the polarizer, and the adjusted pulse pump light Input the third-order nonlinear optical waveguide.

Among them, all devices are arranged in a straight line.

Wherein, the pulsed light source is a passively mode-locked laser, an actively mode-locked laser, a passively Q-switched laser, an actively Q-switched laser, a directly modulated semiconductor laser, or an externally modulated semiconductor laser.

Wherein, the pump filter is a filter or filter combination with a sideband suppression ratio greater than 115 decibels.

Wherein, the pump filter is a circulator plus a fiber grating, a coated optical filter, a MEMS optical filter, a Fabry-Perot optical filter, an arrayed waveguide grating filter, and an optical wavelength division multiplexing device one or any combination of them.

Wherein, the adjustable attenuator is an adjustable attenuator in the form of optical fiber extrusion or coating.

Wherein, the polarizer is an optical fiber polarization beam splitter, a metal-coated optical fiber polarizer, or an optical crystal polarization beam splitter prism.

Wherein, the polarization controller is a polarization controller with an optical fiber output.

Wherein, the polarization controller is a polarization controller wound by an optical fiber, a polarization controller based on optical fiber extrusion, or a half-wave plate and a quarter-wave plate cut from a crystal material with an optical output package. Polarization controller.

Wherein, the third-order nonlinear optical waveguide is: polarization maintaining fiber, microstructure fiber, photonic crystal fiber, sulfide fiber, nano silicon wire waveguide, photonic crystal structure silicon waveguide, gallium arsenide waveguide, or sulfide waveguide.

Wherein, the spectral filtering device is a multi-port filter or a filter combination with a passband isolation greater than 110 decibels.

Wherein, the optical splitting and filtering device is a circulator plus a fiber grating, a coated optical filter, a MEMS optical filter, a Fabry-Perot optical filter, an arrayed waveguide grating filter, and an optical wavelength division multiplexing device. one or any combination of them.

(3) Beneficial effects

The polarization-entangled quantum light source of the present invention utilizes the spontaneous four-wave mixing process in the optical material with third-order optical nonlinearity to generate the same polarization-entangled two-photon. The generation, collection and transmission efficiency of polarization entangled two-photons is high; the simple linear structure is adopted, and there is no need for additional complex time division multiplexing or diversity polarization loops and other devices, and has the advantages of simple structure, stable performance, and easy implementation; using The birefringence properties that can be flexibly designed in nonlinear optical waveguides control the characteristics of nonlinear optical processes, which opens up a new way for the physical realization of simplified polarization-entangled quantum light sources.

Description of drawings

Fig. 1 is a schematic structural diagram of a polarization-entangled quantum light source according to an embodiment of the present invention;

Fig. 2(a)-Fig. 2(d) are schematic diagrams of two kinds of spontaneous four-wave mixing processes that may be excited in the polarization-maintaining dispersion-shifted fiber in the polarization-entangled quantum light source of the embodiment;

3 is a schematic diagram of the physical process of two-photon generation with polarization entanglement characteristics in the polarization-maintaining dispersion-shifted fiber in the polarization-entangled quantum light source of the embodiment;

4 is a schematic diagram of a polarization-entangled two-photon detection device of the polarization-entangled quantum light source of the embodiment;

Fig. 5 is the unilateral counting detection result of idler photons generated by the polarization-entangled quantum light source of the embodiment;

Fig. 6 is a two-photon interference detection result of the polarization-entangled quantum light source of the embodiment.

Detailed ways

The polarization-entangled quantum light source of the present invention is described in detail as follows with reference to the drawings and embodiments.

The core idea of the present invention is: by controlling the polarization state of the pump light, the spontaneous scalar four-wave mixing process can be independently excited on the two polarization axes of the third-order nonlinear optical waveguide with equal intensity; at the same time, using the third-order nonlinear optical waveguide The birefringence characteristic of the waveguide suppresses the spontaneous vector four-wave mixing process in the waveguide, so that the third-order nonlinear optical waveguide outputs polarization-entangled two-photons under pump light excitation.

As shown in Figure 1, a polarization-entangled quantum light source according to an embodiment of the present invention includes:

The pump light generating device (shown by the dotted line box in the figure) is used to generate pulsed pump light and input it to the third-order nonlinear optical waveguide; the third-order nonlinear optical waveguide 6 has birefringence characteristics and is used for The spontaneous scalar four-wave mixing process is independently excited on the two polarization axes to generate signal and idler two-photons, and the spontaneous vector four-wave mixing process is suppressed; the optical splitting filter device 7 is used to output the third-order nonlinear optical waveguide 6 The signal photon, idler sidephoton and pulse pump light are separated, and the selected signal and idler sidephoton have the characteristics of polarization entanglement, that is, polarization-entangled two-photon.

Among them, the third-order nonlinear optical material can be fabricated into a nonlinear optical waveguide 6 with low transmission loss, single spatial mode, and low-loss connection with optical fiber through mature optical microfabrication technology. This process of suppressing spontaneous vector four-wave mixing using the birefringence of the third-order nonlinear optical waveguide 6 includes two possible physical mechanisms: one is to use the birefringence of the third-order nonlinear optical waveguide with birefringence to realize the process of Separation of signal and idler two-photons generated by spontaneous vector four-wave mixing process and signal and idler two-photon generated by spontaneous scalar four-wave mixing process on optical wavelength; selection of spontaneous scalar four-wave mixing process generated by optical filtering The signal and the idler two-photon, while suppressing the signal and the idler two-photon output of the spontaneous vector four-wave mixing process; the second is to use the birefringence in the third-order nonlinear optical waveguide 6 to make the pulse pump injected into the waveguide 6 The two polarization components of the pump light walk away in time-space, because the two polarization components of the pump pulse separated in time-space cannot form a spontaneous vector four-wave mixing process, thereby realizing the spontaneous vector four-wave mixing process suppression.

In addition, the pumping light generating device further includes: a pulsed light source 1 for outputting pulsed pumping light; a pumping filter 2 connected to the output of the pulsed light source 1 for outputting pulsed pumping light other than the wavelength of the pulsed light source 1 The stray light filtering; the adjustable attenuator 3 is used to adjust the power of the pulse pump light output by the pump light filter 2; the polarizer 4 is used to adjust the pulse pump light of the adjustable attenuator 3 The polarization state is transformed into linear polarization; the polarization controller 5 is used to adjust the polarization state of the pulsed pumping light adjusted by the polarizer 4 , and input the adjusted pulsed pumping light into the third-order nonlinear optical waveguide 6 .

The pulsed light source 1 can be any form of light source with pulsed output, such as passive mode-locked laser, active mode-locked laser, passive Q-switched laser, active Q-switched laser, directly modulated semiconductor laser, or externally modulated semiconductor laser, etc.

The pump filter 2 is any filter or filter combination with a sideband suppression ratio greater than 115 decibels, which can be a circulator plus a fiber grating, a coated optical filter, a micro-electromechanical system MEMS optical filter, a Fabry-Pert Any combination of Luo optical filter, arrayed waveguide grating filter and optical wavelength division multiplexing device.

The adjustable attenuator 3 can be any adjustable attenuator in the form of optical fiber extrusion or coating.

The polarizer 4 is any optical device capable of forming a specific polarization state of light, which may be a fiber optic polarization beam splitter, a metal-coated fiber optic polarizer, or an optical crystal polarization beam splitter prism.

The polarization controller 5 is any polarization controller with an optical fiber output, which can be a polarization controller wound by an optical fiber, a polarization controller based on optical fiber extrusion, or a half-wave plate cut from a crystal material with an optical output package and Polarization controller consisting of a quarter-wave plate.

The third-order nonlinear optical waveguide 6 is: polarization maintaining fiber, microstructure fiber, photonic crystal fiber, sulfide fiber, nano silicon wire waveguide, photonic crystal structure silicon waveguide, gallium arsenide waveguide, or sulfide waveguide, etc.

The spectroscopic filtering device 7 is any multi-port filter or filter combination with passband isolation greater than 110 decibels. It can be one or any of circulator plus fiber grating, coated optical filter, MEMS optical filter, Fabry-Perot optical filter, arrayed waveguide grating filter and broadcast division multiplexing device The combination.

Preferably, all devices constituting the polarization-entangled quantum light source of the present invention are arranged in a straight line.

The polarization-entangled quantum light source of the present invention will be further described below through specific examples.

This embodiment is a polarization-entangled quantum light source with a wavelength of 1.5 microns, and its structure is shown in FIG. 1 . Among them, a third-order nonlinear optical waveguide with birefringence characteristics is used as a polarization-maintaining dispersion-shifted fiber. In order to avoid the quantum entanglement decoherence effect caused by fiber birefringence walk-off, the 150-meter-long fiber was divided into two sections of 75 meters, and the two sections were welded with a 90-degree polarization axis offset. Specific parameters of the polarization-maintaining dispersion-shifted fiber are shown in Table 1.

Table 1

The pulse light source selected in this embodiment is a passive mode-locked fiber laser in the 1.5 micron band plus optical filter stretching; the wavelength of the pulsed pump light is 1552.75nm, the line width is 0.2nm, and the repetition frequency is 1MHz; the pump filter uses a circulator It is realized by adding a fiber grating and a coated tunable optical filter, the filtering bandwidth is 0.2nm, and the sideband suppression ratio is greater than 115 decibels; the adjustable attenuator adopts a coated tunable optical attenuator; the polarizer adopts an optical crystal with optical fiber packaging ; The polarization controller is a fiber optic polarization controller wound by optical fiber; the splitting filter device is composed of a waveguide array grating combined with a fiber grating and a coated tunable optical filter, and its suppression of the pump light is greater than 110 decibels. The signal and idler two-photon wavelengths are 1555.15nm and 1550.35nm, respectively.

The physical process of generating polarization-entangled two-photons in a polarization-maintaining dispersion-shifted fiber is shown in Figure 2. Figure 2(a) and Figure 2(b) are schematic diagrams of two spontaneous vector four-wave mixing processes, in which two pump photons with different polarization states are annihilated to generate a pair of signals with different polarization states and idler two-photons. Figure 2(c) and Figure 2(d) are schematic diagrams of two spontaneous scalar four-wave mixing processes, in which two pump photons with the same polarization state are annihilated to generate a pair of signals with the same polarization state and idler two-photons.

In this embodiment, a 150-meter-long polarization-maintaining dispersion-shifted fiber is pumped with short pulses. Due to the high birefringence characteristics of the polarization-maintaining dispersion-shifted fiber, the short-pulse pump light components on the polarization axes of the two fibers walk away quickly, so that the spontaneous vector four-wave mixing process is suppressed. Then only the spontaneous scalar four-wave mixing processes along the two polarization axes are excited in the fiber.

As shown in Figure 3, by adjusting the polarization state of the pump light, the power levels of the pump light components on the polarization axes of the two fibers are consistent, and the intensities of the two spontaneous scalar four-wave mixing processes excited along the polarization axes of the two fibers are equal. The independently generated signal and idler two-photon states overlap in space and time to form polarization-entangled two-photons at 1.5 μm.

The detection of the generated polarization-entangled two-photons is completed by the device shown in the dashed box in Fig. 4 . Signal photons generated by the polarization-entangled quantum light source enter a polarization analyzer composed of a polarization controller 8 , a rotatable half-wave plate 10 and a polarization beam splitter 12 , and then are counted and measured by a single-photon detector 14 . The idler photons enter the polarization analyzer composed of the polarization controller 9 , the rotatable half-wave plate 11 and the polarization beam splitter 13 , and then are counted and measured by the single photon detector 15 . The output remaining pump light is detected by the photodetector 17 and then an electric pulse is output, which is used as a trigger signal of the single photon detector. The output signals of the single photon detector 14 and the single photon detector 15 are sent to the composite counting system 16 for quantum entanglement characteristic analysis.

Figure 5 shows the photon counting results measured by idler photons at different angles of the polarization analyzer. It can be seen that the idler photon count hardly changes with the angle of the polarization analyzer, which demonstrates that the generated two-photon state has the indistinguishable property of a single polarization state. Fig. 6 shows the signal and idler two-photon composite counting results measured at different signal photon polarization analyzer angles when the idler photon polarization analyzer angles are 0 degrees and 135 degrees respectively. It can be seen that the measured signal and idler two-photon recombination counting results show two-photon interference characteristics under non-orthogonal polarization bases, and the interference fringe contrast reaches 92% and 89%, respectively. Thus, the polarization entanglement characteristic of the output two-photon state of the polarization-entangled quantum light source in this embodiment is demonstrated.

The above embodiments are only used to illustrate the present invention, but not to limit the present invention. Those of ordinary skill in the relevant technical field can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, all Equivalent technical solutions also belong to the category of the present invention, and the scope of patent protection of the present invention should be defined by the claims.

Claims (10)

1. a polarization tangles the quantum light source, it is characterized in that, this light source comprises:

The pump light generating means is used for the production burst pump light, and it is inputed to the third-order nonlinear optical waveguide;

The third-order nonlinear optical waveguide, it is divided into two sections, and carry out polarization principal axis 90 and spend the skew weldings, has birefringent characteristic, be used on two polarization axles, independently exciting spontaneous scalar four wave mixing process, generation has signal and the ideler frequency two-photon that polarization tangles characteristic, and two polarized components by making the pulse pump light that is injected in the described third-order nonlinear optical waveguide Space Time walk from, suppress spontaneous vector four wave mixing process, described third-order nonlinear optical waveguide is: polarization maintaining optical fibre, microstructured optical fibers, sulfide optical fiber, the silicon nanowire waveguide, the waveguide of photon crystal structure silicon, the GaAs waveguide, or sulfide waveguide;

The light splitting filter, the light splitting filter is the passband isolation greater than 110 decibels multiport filter or filter combination, be used for signal photon, ideler frequency photon and the pulse pump light of described third-order nonlinear optical waveguide output are separated, obtain polarization and tangle two-photon;

Described pump light generating means further comprises:

Light-pulse generator, be used for output pulse pump light, make pump light component power level unanimity on the two optical fiber polarisation axles by adjusting the pumping polarization state of light, the intensity of the two spontaneous scalar four wave mixing processes that are excited along two optical fiber polarisation direction of principal axis equates that independent signal and the ideler frequency two-photon attitude that produces is overlapping on space-time;

The pumping filter links to each other with the output of described light-pulse generator, is used for the stray light filtering beyond the pulse pump optical wavelength of described light-pulse generator output;

Adjustable attenuator is for the power of the pulse pump light of regulating described pump light filter output;

The polarizer is used for changing the pulse pump polarization state of light after the described adjustable attenuator adjustment into linear polarization;

Polarization Controller be used for adjusting the pulse pump polarization state of light after the described polarizer is adjusted, and the pulse pump light after will adjusting is imported described third-order nonlinear optical waveguide.

2. polarization as claimed in claim 1 tangles the quantum light source, it is characterized in that, all devices linearly type are arranged.

3. polarization as claimed in claim 1 tangles the quantum light source, it is characterized in that, described light-pulse generator be laser with active-passive lock mould, active mode locking laser, passive Q-regulaitng laser, initiatively Q-switched laser, directly transfer semiconductor laser or external modulation semiconductor laser.

4. polarization as claimed in claim 1 tangles the quantum light source, it is characterized in that, described pumping filter is the sideband rejection ratio greater than 115 decibels filter or filter combination.

5. polarization as claimed in claim 4 tangles the quantum light source, it is characterized in that described pumping filter is the combination that circulator adds a kind of or any kind in fiber grating, plated film type optical filter, micro-electromechanical system (MEMS) optical filter, Fabry-Perot optical filter, array waveguide grating filter and the light wavelength division multiplexing device.

6. polarization as claimed in claim 1 tangles the quantum light source, it is characterized in that, described adjustable attenuator is the adjustable attenuator of optical fiber extruding or plated film form.

7. polarization as claimed in claim 1 tangles the quantum light source, it is characterized in that, the described polarizer is the optical fiber polarizer or the optical crystal polarization splitting prism of fibre optic polarizing beam splitter, plating.

8. polarization as claimed in claim 1 tangles the quantum light source, it is characterized in that, described Polarization Controller is the Polarization Controller of band optical fiber output.

9. polarization as claimed in claim 8 tangles the quantum light source, it is characterized in that described Polarization Controller is the Polarization Controller that the Polarization Controller of optical fiber coiling, the half-wave plate that forms based on the Polarization Controller of optical fiber extruding or by the crystalline material cutting of band light output encapsulation and quarter-wave plate are formed.

10. polarization as claimed in claim 1 tangles the quantum light source, it is characterized in that described light splitting filter is the combination that circulator adds a kind of or any kind in fiber grating, plated film type optical filter, micro-electromechanical system (MEMS) optical filter, Fabry-Perot optical filter, array waveguide grating filter and the light wavelength division multiplexing device.

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