CN101398590A - All-optical frequency entangled photon source - Google Patents

Abstract

A full-optical fiber frequency entangled photon source comprises a pulse laser, a Sagnac optical fiber ring, an optical fiber polarization controller, an optical fiber polarization splitter and an optical fiber band-pass filter. The key technical proposal of the invention lies in that quantum state transmitted opposite in the Sagnac optical fiber ring composed of a 50/.50 beam splitter, the optical fiber, the optical fiber polarization controller and an optical fiber circulator is led to meet a pattern matching condition when the 50/.50 beam splitter is coupled, thus obtaining high-purity frequency entangled photon pairs. If two output ports of the Sagnac optical fiber ring are a port 1' and a port 2' respectively, the state of the output photon is frequency entangled state |omegas>1'|omegai>2'+|omegai>1'|omegas>2', i.e. when a signal photon is output from the port 1', idle photon occurs at the port 2', and vice versa. The frequency entangled photon source is a switch-type integrated light quantum device, composed of optical fiber devices, and can be widely applied to the fields of fundamental physics study, quantum key distribution, quantum logic gate, interaction of light and atom and the like.

Description

All-optical frequency entangled photon source

[technical field]: the invention belongs to the quantum information science technical field, is a kind of frequency entangled photons source.

[background technology]: quantum entanglement is meant the non-local association between physically separable many subsystems quantized system, also promptly can't be independent of the measurement parameter of other subsystem to the measurement result of a subsystem.Quantum entanglement is not only and can be used for checking the quantum mechanics philosophy, still realizes the essential tool of quantum information processing (as quantum calculation, quantum is stealthy to pass attitude, and quantum secret communication).The particle that formation is tangled can have a variety of, as atom, and ion etc., but because the transport property of photon uniqueness, entangled photons is more suitable for transmission of quantum information.

The degree of freedom that can tangle between photon has a lot, for example the orthogonal amplitude of polarization, momentum and position, frequency and light field and position phase component etc.These abundant degree of freedom not only provide convenience for the root problem of research quantum physics, and also the Code And Decode for the quantum information technology provides convenience.

The optical parameter process that studies show that of decades is a kind of effective method that produces the quantum entangled photons.Utilize crystal second nonlinear χ ⁽²⁾The transfer process generation is the method a kind of commonly used that produces entangled photons under the spontaneous radiation optics parameter of effect, produce the entangled photons of multiple degree of freedom by this method, comprised the orthogonal amplitude and the position phase component etc. of polarization, energy and time, momentum and position, frequency and light field.What the quantum information experiment of the majority of having finished was adopted all is the entangled photons that utilizes this method to produce.Yet, because pattern match, with this related photon efficiently coupled into optical fibres store, control and when transmitting, implement very difficulty on the engineering.By comparison, based on optical fiber Ke Er third-order non-linear χ ⁽³⁾The related photon that the four-wave mixing parametric process of effect produces is right, and is single and be convenient to and the optical fiber coupling because of its transmission mode, embodied remarkable advantages.Utilize the spontaneous four-wave mixing process in the optical fiber to produce multiple entangled photons at present, these degree of freedom comprise the orthogonal amplitude and the position phase component of polarization, energy and time series and light field.With crystal second nonlinear χ ⁽²⁾The entangled photons that the spontaneous radiation optics parametric process of effect is produced is compared, and is abundant not enough based on the degree of freedom of the entangled photons of optical fiber.For effectively utilize based on the entangled photons of optical fiber storage, control and transmission aspect advantage, be necessary to invent and utilize optical fiber to produce the high-quality entangled photons source of various degree of freedom.

[summary of the invention]: the present invention seeks to solve prior art exists or engineering on implement very difficulty, or the abundant not enough problem of the degree of freedom of entangled photons provides a kind of all-optical frequency entangled photon source.

The invention provides a kind of method of utilizing optical fiber to produce the frequency entangled photons, can be used for realizing light and atomic interaction and continuous variable single photon quantum communication.

It is ω that the present invention adopts a centre frequency _pThe laser pulse pumping by 50/.50 beam splitter, the Sagnac fiber optic loop that optical fiber, optical fiber polarization controller and circulator constitute with special synergistic effect, the right signal of the twin photon that makes the laser pump (ing) pulse produce by spontaneous four-wave mixing in optical fiber is exported from two of the Sagnac fiber optic loop different ports respectively with idle photon, rather than from same port output.If two output ports of Sagnac fiber optic loop are respectively port one ' and port 2 ', then the state of output photon is that frequency is tangled attitude | ω _{s 1 '}| ω _{i 2 '}+ | ω _{i 1 '}| ω _{s 2 '}, wherein, ω _sAnd ω _iThe frequency of representing signal photon and idle photon respectively.Also promptly: when the signal photon | ω _sFrom port one ' when exporting, the idle photon that it is twin | ω _iNecessarily appear at port 2 ', vice versa.

Key of the present invention be to invent a kind of can be in the Sagnac fiber optic loop of any splitting ratio, the transmission of quantum attitude satisfies the principle and the method for pattern match when 50/.50 beam splitter is coupled in opposite directions, and has invented on this basis and can produce the right all-optical frequency entangled photon source of frequency entangled photons.

All-optical frequency entangled photon source provided by the invention comprises successively:

Pump light light source: be used to produce pump light;

95/5 beam splitter: be used for 95% pump light is imported the Sagnac fiber optic loop, the pump light with 5% monitors pump power;

The Sagnac fiber optic loop: be made of circulator, 50/.50 beam splitter, optical fiber and first optical fiber polarization controller successively, wherein, circulator is used for the photon output with the reflection of Sagnac fiber optic loop; 50/50 beam splitter be used to separate pump light and to the photon of transmission in opposite directions to being coupled; It is right that optical fiber is used to produce the twin photon of quantum association;

First optical fiber polarization controller is used for the compensated optical fiber birefringence and introduces phase shift;

Fiber selection zero dispersion shift fiber or microstructured optical fibers in this Sagnac fiber optic loop are used to produce quantum and close

The twin photon of connection is right; The pump photon that two centre frequencies are ω p is by zero dispersion shift fiber or microstructure

It is twin that the scattering simultaneously of the spontaneous four-wave mixing process of optical fiber is that frequency is respectively flashlight and the idle light of ω s and ω i

Third contact of a total solar or lunar eclipse is right, wherein 2 ω _p=ω _s+ ω _i, this parametric process satisfies energy conservation and momentum conservation condition.

90/10 beam splitter: be used for injecting reference signal light and output scattered photon to the Sagnac fiber optic loop;

The 3rd optical fiber polarization controller: be connected with 90% end of 90/10 beam splitter, be used to adjust polarization via 90/10 beam splitter output photon;

First fibre optic polarizing beam splitter: be connected with the 3rd optical fiber polarization controller, be used to select the polarization of output photon;

First flashlight, idle light and pump light bandpass filter: be connected with first fibre optic polarizing beam splitter, the signal that is used for being produced by spontaneous four-wave mixing in the optical fiber separates with pump light with idle photon, the light output that selection is consistent with flashlight and idle light center frequency;

The 4th optical fiber polarization controller: be connected with the circulator in the Sagnac fiber optic loop, be used to adjust the polarization of the photon of the Sagnac fiber optic loop reflection of exporting by circulator;

Second fibre optic polarizing beam splitter: be connected with the 4th optical fiber polarization controller, be used to select the polarization of output photon;

Secondary signal light, idle light and pump light bandpass filter: be connected with second fibre optic polarizing beam splitter, the signal that is used for being produced by spontaneous four-wave mixing in the optical fiber separates with pump light with idle photon, the light output that selection is consistent with flashlight and idle light center frequency.

The composition of described pump light light source comprises successively:

Optical fiber femtosecond laser; Be used for output laser pulse;

The first pump light bandpass filter: connect optical fiber femtosecond laser, be used for eliminating frequency that pumping laser comprises photon (transmission port) at ω s and ω i wave band;

Fiber amplifier: be connected with the pump light bandpass filter, be used to amplify the power of the laser pulse of first pump light bandpass filter transmission port output;

The second pump light bandpass filter: be connected with fiber amplifier, be used for eliminating wavelength that pumping laser comprises photon, and the pumping laser of transmission end output is input to 95/5 beam splitter at ω s and ω i wave band.

Entangled photons provided by the invention source also comprises a reference signal radiant that is used to produce the Adjustment System parameter, and its composition comprises successively:

Optical fiber femtosecond laser: be used for output laser pulse;

The first pump light bandpass filter: connect optical fiber femtosecond laser, be used to extract frequency not at the photon (reflector port) of pump light centre frequency ω p wave band;

The flashlight bandpass filter: be connected with the first pump light bandpass filter reflector port, be used to extract frequency at the light of ω i wave band as the reference flashlight;

Second optical fiber polarization controller: be connected with 10% end of 90/10 beam splitter, be used to adjust the reference signal polarisation of light that injects 90/10 beam splitter.

The debugging in principle of work of the present invention and entangled photons source

(1) principle of work of all-optical frequency entangled light source

As shown in Figure 1, the Sagnac fiber optic loop is made up of 50/50 beam splitter, optical fiber (solid line among Fig. 1) and optical fiber polarization controller, optical fiber polarization controller can be used to control with compensated optical fiber in birefringence.We suppose optical fiber for not introducing birefringent ideal fiber, and the effect of optical fiber polarization controller is the control phase shift.

If the Sagnac fiber optic loop is in the xz plane shown in coordinate among Fig. 1, the incident laser pumping pulse from port one along z direction input optical fibre, through being divided into two-beam behind 50/50 beam splitter, be coupled to port 3 and 4 respectively, the light of entry port 4 has the phase delay of pi/2 with respect to the light of port 3.The two-beam of port 4 and port 3 transmits in opposite directions along clockwise and counter clockwise direction respectively, and then coupling outputs to port one at 50/50 beam splitter place ' and port 2 '.

If the light field of incident laser pumping pulse is $\stackrel{\→}{E}{p}_1=\stackrel{\→}{x}E{p}_{1x}+\stackrel{\→}{y}E{p}_{1y},$ Wherein

The denotation coordination direction, Ep _1x(Ep _1y) represent that the incident laser pumping pulse exists The light field component of direction, if 50/50 fiber optic splitter is lossless, the pumping light field of transmission in opposite directions then $\stackrel{\→}{E}{p}_{3\left(4\right)}=\stackrel{\→}{x}E{p}_{3\left(4\right)x}+\stackrel{\→}{y}E{p}_{3\left(4\right)y}$ Can be expressed as:

$\left(\begin{array}{c}{\mathrm{Ep}}_{3x}\\ {\mathrm{Ep}}_{3y}\\ {\mathrm{Ep}}_{4x}\\ {\mathrm{Ep}}_{4y}\end{array}\right)=\frac{1}{\sqrt{2}}\left(\begin{array}{cc}1& 0\\ 0& 1\\ e^{i\frac{\mathrm{\π}}{2}}& 0\\ 0& e^{i\frac{\mathrm{\π}}{2}}\end{array}\right)\left(\begin{array}{c}{\mathrm{Ep}}_{1x}\\ {\mathrm{Ep}}_{1y}\end{array}\right)---\left(1\right)$

Be divided into two sections for encircling inner fiber for simplicity: ab section and bc section.According to coordinate among Fig. 1, light field is through the ab section time, and the x component can reindexing.Be equivalent to process $\left(\begin{array}{cc}-1& 0\\ 0& 1\end{array}\right)$ Transmission matrix.Suppose that the birefringence in the optical fiber only introduced by Polarization Controller, and Polarization Controller is positioned at the bc section.If for the light field along clockwise transmission, the Jones matrix of equal value of optical fiber polarization controller is $J_C=\left(\begin{array}{cc}{J}_{\mathrm{xx}}& J_{\mathrm{xy}}\\ J_{\mathrm{yx}}& J_{\mathrm{yy}}\end{array}\right),$ The Jones matrix that then counterclockwise transmits light field is its transposition ${\tilde{J}}_C=\left(\begin{array}{cc}{J}_{\mathrm{xx}}& J_{\mathrm{yx}}\\ J_{\mathrm{xy}}& J_{\mathrm{yy}}\end{array}\right).$ If the two bundles pumping light field of transmission in opposite directions can be designated as when 50/50 beam splitter is coupled again

Then $\stackrel{\→}{E}{p\′}_{3\left(4\right)}=\stackrel{\→}{x}E{p\′}_{3\left(4\right)x}+\stackrel{\→}{y}E{p\′}_{3\left(4\right)y}$ Can be expressed as

$\left(\begin{array}{c}E{p}_{3x}^{\′}\\ {\mathrm{Ep}}_{3y}^{\′}\end{array}\right)=\left(\begin{array}{cc}{J}_{\mathrm{xx}}& J_{\mathrm{xy}}\\ J_{\mathrm{yx}}& J_{\mathrm{yy}}\end{array}\right)\left(\begin{array}{cc}-1& 0\\ 0& 1\end{array}\right)\left(\begin{array}{c}{\mathrm{Ep}}_{3x}\\ {\mathrm{Ep}}_{3y}\end{array}\right)$

$\left(\begin{array}{c}E{p}_{4x}^{\′}\\ {\mathrm{Ep}}_{4y}^{\′}\end{array}\right)=\left(\begin{array}{cc}-1& 0\\ 0& 1\end{array}\right)\left(\begin{array}{cc}{J}_{\mathrm{xx}}& J_{\mathrm{yx}}\\ J_{\mathrm{xy}}& J_{\mathrm{yy}}\end{array}\right)\left(\begin{array}{c}{E}_{4x}\\ E_{4y}\end{array}\right)---\left(2\right)$

As calculated as can be known:

${\mathrm{Ep}}_{3x}^{\′}=\frac{1}{\sqrt{2}}(-J_{\mathrm{xx}}{\mathrm{Ep}}_{1x}+J_{\mathrm{xy}}{\mathrm{Ep}}_{1y})$

${\mathrm{Ep}}_{3y}^{\′}=\frac{1}{\sqrt{2}}(-J_{\mathrm{yx}}{\mathrm{Ep}}_{1x}+J_{\mathrm{yy}}{\mathrm{Ep}}_{1y})$

　　　　　　　　　　　　　　　(3)

${\mathrm{Ep}}_{4x}^{\′}=\frac{1}{\sqrt{2}}{e}^{i\frac{\mathrm{\π}}{2}}(-J_{\mathrm{xx}}{\mathrm{Ep}}_{1x}-J_{\mathrm{yx}}{\mathrm{Ep}}_{1y})$

${\mathrm{Ep}}_{4y}^{\′}=\frac{1}{\sqrt{2}}{e}^{i\frac{\mathrm{\π}}{2}}(J_{\mathrm{xy}}{\mathrm{Ep}}_{1x}+J_{\mathrm{yy}}{\mathrm{Ep}}_{1y})$

Suppose light field Ep ' ₃And Ep ' ₄Pattern match, because of spatial model matching condition in the optical fiber satisfies automatically, so also be that the polarization direction is identical, both sides relation can be expressed as ${\stackrel{\→}{E}}_4^{\′}=e^{\mathrm{i\φ}}{\stackrel{\→}{E}}_3^{\′},$ Wherein φ is both phasic differences.So, two-beam is in the coupling again of 50/50 fiber optic splitter, is equal to free space 50/50 beam splitter through as shown in Figure 2 on the principle.The output Ep of its pump field ₁' and Ep ₂' be

${\stackrel{\&RightArrow;}{E}p}_1^{\&prime;}=\frac{1}{\sqrt{2}}(e^{i\frac{\mathrm{\&pi;}}{2}}{\stackrel{\&RightArrow;}{E}\mathrm{<figure-callout\; id="3"\; label="p"\; filenames="A200810152844E00191.png"\; state="\{\{state\}\}">p</figure-callout>}}_3^{\&prime;}+{\stackrel{\&RightArrow;}{E}p}_4^{\&prime;})$

(4)

${\stackrel{\&RightArrow;}{E}p}_2^{\&prime;}=\frac{1}{\sqrt{2}}({\stackrel{\&RightArrow;}{E}\mathrm{<figure-callout\; id="3"\; label="p"\; filenames="A200810152844E00191.png"\; state="\{\{state\}\}">p</figure-callout>}}_3^{\&prime;}+e^{i\frac{\mathrm{\&pi;}}{2}}{\stackrel{\&RightArrow;}{E}p}_4^{\&prime;})$

On the basis of analyzing the pump light state, can further analyze the right state of photon in the Sagnac fiber optic loop.Chuan Shu two-beam in opposite directions $\left|{\mathrm{<figure-callout\; id="3"\; label="Ep"\; filenames="A200810152844E00191.png"\; state="\{\{state\}\}">Ep</figure-callout>}}_3\right|=\left|{\mathrm{Ep}}_4\right|=\frac{\sqrt{2}}{2}\left|{\mathrm{Ep}}_1\right|,$ It is right all to produce signal and the idle photon consistent with its polarization by spontaneous four-wave mixing process with certain probability | ω _{s 3}| ω _{i 3}With | ω _{s 4}| ω _{i 4}, wherein subscript 3 (or 4) expression photon is along (contrary) clockwise to the direction of propagation in the Sagnac fiber optic loop.Because the phase information that photon carries pump photon to meeting, therefore the photon of transmission is 2 φ to phasic difference in opposite directions.In this case, for signal and idle photon to, the input state of Sagnac fiber optic loop can be expressed as

Wherein η is the coefficient relevant with four-wave mixing gain in the optical fiber.If when 50/50 fiber optic splitter place recombination, photon is to state | ω _{s 3}| ω _{i 3}With | ω _{s 4}| ω _{i 4}Pattern is mated fully, and then the output state of Sagnac fiber optic loop then can be expressed as [annotate 1, annotate 2]

Wherein, two output ports of Sagnac fiber optic loop in subscript 1 ' and the 2 ' presentation graphs 1.By formula (5) as can be known, when $\mathrm{\&phi;}=\frac{\mathrm{\&pi;}}{2}$ Or $\mathrm{\&phi;}=\frac{3\mathrm{\&pi;}}{2}$ The time, output state

And when φ=0 or φ=π, output state

In the previous case, non-degenerate signal of a pair of frequency and the idle photon that produces by same laser pump (ing) pulse | ω _sAnd | ω _iExport by the same port of Sagnac fiber optic loop.Under latter event, although for any one signal or idle photon, it can appear at any one output port randomly, but export by the different port of Sagnac fiber optic loop respectively by a pair of signal and idle photon that same laser pump (ing) pulse produces: when the signal photon appears at port one ' time, then idle photon appears at port 2 ', when idle photon appeared at port 2 ', then the signal photon appeared at port one '; At this moment, for each signal and the idle photon of Sagnac fiber optic loop output, can't distinguish it is by clockwise or the pump light of counterclockwise propagating produces, and this indistinguishability is the right root of generation frequency entangled photons.

According to formula (5), the generation of frequency entangled photons requires to satisfy condition 2 φ=2n π, and wherein n is an integer.Because light field Ep ' ₃And Ep ' ₄The polarization direction is identical, when φ=0, ${\mathrm{Ep}}_{3x}^{\&prime;}={\mathrm{Ep}}_{4x}^{\&prime;},$ ${\mathrm{Ep}}_{3y}^{\&prime;}={\mathrm{Ep}}_{4y}^{\&prime;},$ Corresponding pump field is output as $\stackrel{\&RightArrow;}{E}{p}_1^{\&prime;}=\frac{1}{\sqrt{2}}{\stackrel{\&RightArrow;}{E}}_{\mathrm{<figure-callout\; id="3"\; label="p"\; filenames="A200810152844E00191.png"\; state="\{\{state\}\}">p</figure-callout>}3}^{\&prime;}(e^{i\frac{\mathrm{\&pi;}}{2}}+1),$ ${\stackrel{\&RightArrow;}{E}p}_2^{\&prime;}=\frac{1}{\sqrt{2}}{\stackrel{\&RightArrow;}{E}}_{\mathrm{<figure-callout\; id="3"\; label="p"\; filenames="A200810152844E00191.png"\; state="\{\{state\}\}">p</figure-callout>}3}^{\&prime;}(1+e^{i\frac{\mathrm{\&pi;}}{2}});$ When φ=π, ${\mathrm{Ep}}_{3x}^{\&prime;}={-\mathrm{Ep}}_{4x}^{\&prime;}{\mathrm{Ep}}_{3y}^{\&prime;}={-\mathrm{Ep}}_{4y}^{\&prime;},$ Corresponding pump field is output as ${\stackrel{\&RightArrow;}{E}p}_1^{\&prime;}=\frac{1}{\sqrt{2}}\stackrel{\&RightArrow;}{E}{\mathrm{<figure-callout\; id="3"\; label="p"\; filenames="A200810152844E00191.png"\; state="\{\{state\}\}">p</figure-callout>}}_3^{\&prime;}(e^{i\frac{\mathrm{\&pi;}}{2}}-1),$ $\stackrel{\&RightArrow;}{E}{p}_2^{\&prime;}=\frac{1}{\sqrt{2}}\stackrel{\&RightArrow;}{E}{\mathrm{<figure-callout\; id="3"\; label="p"\; filenames="A200810152844E00191.png"\; state="\{\{state\}\}">p</figure-callout>}}_3^{\&prime;}(1-e^{i\frac{\mathrm{\&pi;}}{2}}).$ Above-mentioned analysis explanation, the photon that tangles when Sagnac fiber optic loop output frequency to the time, transmitted light and reflected light

With

Power equal (splitting ratio of Sagnac fiber optic loop is 50%) and polarization state are identical.Therefore, in principle, transmitted light that can be by pump field in the control Sagnac fiber optic loop and polarization of reflected light attitude and power satisfy the condition that the generation frequency is tangled.

(2) pattern match realizes and the right output of frequency entangled photons in the Sagnac fiber optic loop

Above-mentioned analysis be optical fiber do not introduce birefringence and the effect of optical fiber polarization controller be control phase shift hypothesis under obtain, but actually, any optical fiber, comprise that all there is birefringence in various degree inevitably in single-mode fiber, not only the polarization of the pump field of transmission can change along with environment in the Sagnac fiber optic loop, and it exports the transmitted light of pump field and the polarization of polarization of reflected light attitude cannot compare.Also promptly: the precondition of desired pattern match can not be met usually in the formula (5).So we need analyze how to realize photon to pattern match in the Sagnac of reality fiber optic loop, thereby it is right to produce high-purity frequency entangled photons.

The basic thought of implementation pattern coupling is to utilize Polarization Controller, not only introduces phase shift, and birefringence that can compensated optical fiber.Polarization Controller can be considered a plurality of wave plate combined as shown in Figure 3, supposes that wave plate combined is followed successively by clockwise

Wherein $\mathrm{\&lambda;}(=\frac{2\mathrm{\&pi;c}}{{\mathrm{\&omega;}}_p},$ C is the light velocity in the vacuum) expression pumping light wavelength.

Relevant with the polarization of incident light attitude, be used for the birefringence of compensated optical fiber, will pass through The pump light of wave plate becomes the line polarisation.If the phase differential of incident pumping light field x direction and y durection component is α, then

Wherein Ep represents the amplitude of incident pump light,

Be pump light and x axle clamp angle.When

The relative phase shift of introducing equals-during α,

With

Just combine and the pumping light field of random polarization state can be become along the line polarisation of x or y direction polarization.Since in opposite directions transmission, along x or y direction polarized pump light field process

With

The order difference, therefore can between two-beam, introduce relative phase difference

Consider the pump light Ep of input ₁After through 50/50 beam splitter, Chuan Shu Ep in opposite directions ₃And Ep ₄Between have

Phase shift, might satisfy φ=0 or φ=π this moment.

If each wave plate among Fig. 3

Fast axle be followed successively by with x direction of principal axis angle

For the pumping light field of clockwise propagation, the Jones matrix of equal value of Polarization Controller is

$J_c=\left(\begin{array}{cc}{J}_{\mathrm{xx}}& J_{\mathrm{xy}}\\ J_{\mathrm{yx}}& J_{\mathrm{yy}}\end{array}\right)=\left(\begin{array}{cc}{e}^{\mathrm{i\&alpha;}}& 0\\ 0& 1\end{array}\right)\left(\begin{array}{cc}\cos {2\mathrm{\&theta;}}_2& \sin {2\mathrm{\&theta;}}_2\\ \sin {2\mathrm{\&theta;}}_2& -\cos {2\mathrm{\&theta;}}_2\end{array}\right)\left(\begin{array}{cc}1& 0\\ 0& e^{i\frac{\mathrm{\&pi;}}{2}}\end{array}\right)\left(\begin{array}{cc}0& 1\\ 1& 0\end{array}\right)\left(\begin{array}{cc}\cos {2\mathrm{\&theta;}}_1& \sin {2\mathrm{\&theta;}}_1\\ \sin {2\mathrm{\&theta;}}_1& -{\cos 2\mathrm{\&theta;}}_1\end{array}\right)\left(\begin{array}{cc}{e}^{\mathrm{i\&alpha;}}& 0\\ 0& 1\end{array}\right)$

$=\left(\begin{array}{cc}{e}^{i2\mathrm{\&alpha;}}(\cos {2\mathrm{\&theta;}}_2\sin {2\mathrm{\&theta;}}_1+\sin {2\mathrm{\&theta;}}_2\cos {2\mathrm{\&theta;}}_1{e}^{i\frac{\mathrm{\&pi;}}{2}})& e^{i\mathrm{\&alpha;}}(-\cos {2\mathrm{\&theta;}}_2\cos {2\mathrm{\&theta;}}_1+\sin {2\mathrm{\&theta;}}_2\cos {2\mathrm{\&theta;}}_1{e}^{i\frac{\mathrm{\&pi;}}{2}})\\ e^{i\mathrm{\&alpha;}}(\sin {2\mathrm{\&theta;}}_2\sin {2\mathrm{\&theta;}}_1-\cos {2\mathrm{\&theta;}}_2\cos {2\mathrm{\&theta;}}_1{e}^{i\frac{\mathrm{\&pi;}}{2}})& -\sin {2\mathrm{\&theta;}}_2\cos {2\mathrm{\&theta;}}_1-\cos {2\mathrm{\&theta;}}_2\sin {2\mathrm{\&theta;}}_1{e}^{i\frac{\mathrm{\&pi;}}{2}}\end{array}\right)---\left(6\right)$

With formula (6) substitution formula (3), and analyze when φ=0th,, wave plate combined satisfies ${\mathrm{Ep}}_{3x}^{\&prime;}={\mathrm{Ep}}_{4x}^{\&prime;},$ ${\mathrm{Ep}}_{3y}^{\&prime;}={\mathrm{Ep}}_{4y}^{\&prime;},$ And during φ=π, wave plate combined satisfies ${\mathrm{Ep}}_{3x}^{\&prime;}={-\mathrm{Ep}}_{4x}^{\&prime;},$ ${\mathrm{Ep}}_{3y}^{\&prime;}={-\mathrm{Ep}}_{4y}^{\&prime;}$ Condition.

When φ=0, ${\mathrm{Ep}}_{3x}^{\&prime;}={\mathrm{Ep}}_{4x}^{\&prime;},$ ${\mathrm{Ep}}_{3y}^{\&prime;}={\mathrm{Ep}}_{4y}^{\&prime;},$ The time, can obtain following equation:

Equation (7) and (8) separate for:

N wherein, m is an integer.As m=n=0 or m=0, during n=1, can get following particular solution:

In like manner, when φ=π, ${\mathrm{Ep}}_{3x}^{\&prime;}={-\mathrm{Ep}}_{4x}^{\&prime;}{\mathrm{Ep}}_{3y}^{\&prime;}={-\mathrm{Ep}}_{4y}^{\&prime;}$ The time, can obtain following equation:

Equation (11) and (12) separate for:

As m=n=0 or m=0, during n=1, can get following particular solution:

By formula (9)-(14) as can be known, although the birefringence meeting that exists in the optical fiber influences photon required satisfied pattern match when being coupled at 50/50 beam splitter place, but by suitably adjusting the Polarization Controller in the Sagnac fiber optic loop, can be in the birefringent while of compensated optical fiber, the parameter in the control formula (5) , it is right to obtain high-purity frequency entangled photons.

Be difficult to comparison in order to solve Sagnac fiber optic loop output pump field transmitted light and polarization of reflected light attitude polarization, thereby make the difficulty that pattern match is difficult to realize, can consider port 2 inputs of flashlight from the Sagnac fiber optic loop.When signal polarisation of light and pump light were consistent in the Sagnac fiber optic loop, the four-wave mixing gain of flashlight was maximum.So under the condition of four-wave mixing gain maximum, the polarization that is exaggerated signal reflection of light (transmission) field and pumping optical transmission (reflection) field also is consistent.Therefore, can be by the splitting ratio of control Sagnac ring, and make pump light transmission (reflection) and be exaggerated flashlight and realize producing frequency with the consistent method of reflection (transmission) field polarization and tangle required satisfied pattern match.

(3) device---the debugging in entangled photons source of implementation pattern coupling

As shown in Figure 4, the light that optical fiber femtosecond laser 1 is sent through the first pump light bandpass filter 2 and bandpass filter 20 after, obtain the pump light and the signal pulse of picosecond.Obtain the laser pump (ing) pulse after the light process fiber amplifier 3 of the first pump light bandpass filter, 2 transmission ports output and the second pump light bandpass filter 4.The laser pump (ing) pulse is imported by optical fiber 8, first optical fiber polarization controller 9, in the time of Sagnac fiber optic loop that 50/50 beam splitter 7 and circulator 6 constitutes 12, the reference signal light of path and laser pump (ing) pulse coupling is injected Sagnac fiber optic loop 12 by 90/10 beam splitter 10.Because in the parametric process of four-wave mixing, in the Sagnac fiber optic loop, the flashlight consistent with the pump light polarization can obtain amplifying, make pump light consistent in the Sagnac fiber optic loop with the signal polarisation of light so regulate second optical fiber polarization controller 11, this moment is at port one ' can be observed with port 2 ' and be exaggerated and flashlight that polarization is consistent with pump light.Adjust the 3rd optical fiber polarization controller 13 then, feasible pumping light power minimum (power meter 18 numerical value minimums) by first fibre optic polarizing beam splitter 14 and first bandpass filter 15; Then, adjust first optical fiber polarization controller 9 again, not only make pumping light power (numerical value of power meter 19) be maximum 50% of the power that passes through by second bandpass filter 16, and make signal light power also minimum (power meter 17 numerical value minimums) by the 3rd optical fiber polarization controller 13, the first fibre optic polarizing beam splitters 14 and first bandpass filter 15.This moment is identical with flashlight mirror field polarization by the pump light transmitted field of port 2 ', and Chuan Shu photon satisfies the condition of pattern match to when 50/50 beam splitter 7 is coupled in opposite directions.

After the pattern match adjustment is finished, with the input disconnection of reference signal light, at reflector port 1 ' access the 4th optical fiber polarization controller 21 and second fibre optic polarizing beam splitter 22 of circulator 6, as shown in Figure 5.Adjust the 3rd, the 4th optical fiber polarization controller 13 and 21, feasible parallel with pump light with the polarization of the scattered photons of 22 outputs from first, second fibre optic polarizing beam splitter 14, the signal that passes through first, second bandpass filter 15 and 16 and the idle photon of Sagnac fiber optic loop output this moment are right to being the frequency entangled photons

Rather than

Advantage of the present invention and good effect:

The present invention is an all-optical frequency entangled photon source, core devices wherein is to have a special nature sagnac fiber optic loop by what optical fiber and 50/50 fiber optic splitter and optical fiber polarization controller constituted, make and export from the different output port of sagnac fiber optic loop respectively with idle photon by a pair of frequency nondegenerate signal that the spontaneous four-wave mixing process in the optical fiber produces, thereby obtain the photon that frequency is tangled by the laser pump (ing) pulse.The photon of ' and port 2 ', then ought appear at port one ' is the flashlight period of the day from 11 p.m. to 1 a.m if two output ports of sagnac fiber optic loop are respectively port one, and its twin idle photon necessarily appears at d port 2 ', and vice versa.

Tangle with the polarization that utilizes optical fiber to produce and the entangled photons in finite dimension ket spaces such as energy and time series to comparing [annotating 3], the ket space of the all-optical frequency entangled light source of the present invention is infinite dimension continuous variable; The frequency entangled photons that produces with the existing second order nonlinear effect that utilizes crystal is to comparing, the all-optical frequency entangled light source of the present invention has the pure advantage of pattern, and optional usefulness has the photonic crystal fiber of different dispersion characteristics, and the frequency entangled photons that produces different-waveband neatly is right; In addition, owing to adopt all optical fibre structure, so the present invention also has little, the easy-operating advantage of volume.These advantages make the present invention have a wide range of applications at light and atomic interaction and continuous variable single photon quantum communication field.

[description of drawings]:

Fig. 1 is light field transmission principle figure in the Sagnac fiber optic loop;

Fig. 2 is the schematic diagram of free space 50/50 beam splitter light field stack;

Fig. 3 is a light field polarization variations schematic diagram in the Sagnac fiber optic loop;

Fig. 4 realizes producing the adjusting gear that frequency is tangled in the Sagnac fiber optic loop;

Fig. 5 is the device of all-optical frequency entangled photon source;

Fig. 6 (a) is in the all-optical frequency entangled photon source, from the single channel counting of Sagnac fiber optic loop same output port measuring-signal photon and idle photon and the device of coincidence counting; (b) be the frequency spectrum of first bandpass filter 15 at the flashlight passage; (c) be the frequency spectrum of first bandpass filter 15 at idle optical channel; (d) be measurement result;

Fig. 7 (a) is in the all-optical frequency entangled photon source, from the single channel counting of different output port measuring-signal photons of Sagnac fiber optic loop and idle photon and the device of coincidence counting; (b) be measurement result;

Fig. 8 is that the demonstration frequency is tangled the device of quantum interference;

Fig. 9 is the graph of a relation of single-photon detector coincidence counting and accurate translation stage position.

Among the figure, 1. optical fiber femtosecond laser; 2. the first pump light bandpass filter; 3. fiber amplifier; 4. the second pump light bandpass filter; 5.95/5 beam splitter; 6. circulator; 7.50/50 beam splitter; 8. optical fiber; 9. first optical fiber polarization controller; 10.90/10 beam splitter; 11. second optical fiber polarization controller; 12.Sagnac fiber optic loop; 13. the 3rd optical fiber polarization controller; 14. first fibre optic polarizing beam splitter; 15. first flashlight, pump light and idle optical band pass filter; 16. secondary signal light, pump light and idle optical band pass filter; 17. power meter; 18. power meter; 19. power meter; 20. flashlight bandpass filter; 21. the 4th optical fiber polarization controller; 22. second fibre optic polarizing beam splitter; 23 and 24 single-photon detectors; 25, the single photon counting system; 26.50/50 fiber optic splitter; 27. optical fiber polarization controller; 28. the time-delay mechanism that constitutes by catoptron and accurate translation stage.

[embodiment]:

Embodiment 1: all-optical frequency entangled photon source is formed

As shown in Figure 5, all-optical frequency entangled photon source provided by the invention comprises successively:

Pump light light source: be used to produce pump light; Comprise successively: optical fiber femtosecond laser 1, the first pump light bandpass filter 2, fiber amplifier 3, the second pump light bandpass filter 4.

Reference signal radiant: be used to produce reference signal light; Comprise successively: optical fiber femtosecond laser 1, the first pump light bandpass filter 2, flashlight bandpass filter 20.

95/5 beam splitter 5 and constitute Sagnac fiber optic loop 12 by circulator 6,50/.50 beam splitter 7, optical fiber 8 and first optical fiber polarization controller 9 successively, optical fiber 8 is selected zero dispersion shift fiber or microstructured optical fibers for use, and the twin photon that is used to produce the quantum association is right; It is right that the spontaneous four-wave mixing process simultaneously scattering of the pump photon that two centre frequencies are ω p by zero dispersion shift fiber or microstructured optical fibers is that frequency is respectively flashlight and the twin photon of idle light of ω s and ω i, wherein 2 ω _p=ω _s+ ω _i, this parametric process satisfies energy conservation and momentum conservation condition.

90/10 beam splitter 10, second optical fiber polarization controller 11, the 3rd optical fiber polarization controller 13, first fibre optic polarizing beam splitter 14, with first flashlight, pump light and idle optical band pass filter 15, and the 4th optical fiber polarization controller 21, the second fibre optic polarizing beam splitters 22 and secondary signal light, pump light and idle optical band pass filter 16.

The concrete debug process of above all-optical frequency entangled photon source is omited with the summary of the invention part herein.

Embodiment 2:

The output state of all-optical frequency entangled photon source is

Rather than

Shown in Fig. 6 (a), the pulsewidth of the laser of laser instrument 1 output is 70fs, and centre wavelength and spectrum width are respectively 1550nm and 50nm.The Sagnac fiber optic loop is made of optical fiber (300 meters place the zero-dispersion wavelength of liquid nitrogen is the zero dispersion shift fiber of 1538 nanometers) 8 and 50/50 fiber optic splitter 7, optical fiber polarization controller 9 and fiber optical circulator 6.Through wave filter 2, the centre wavelength of the pump light that amplifier 3 and wave filter 4 obtain $\mathrm{\&lambda;}(=\frac{2\mathrm{\&pi;c}}{{\mathrm{\&omega;}}_p})$ Be respectively 1538.2 nanometers and 5 psecs with bandwidth.Centre wavelength is respectively $\mathrm{\&lambda;s}=\frac{2\mathrm{\&pi;c}}{{\mathrm{\&omega;}}_s}=1544.5$ Nanometer and $\mathrm{\&lambda;i}=\frac{2\mathrm{\&pi;c}}{{\mathrm{\&omega;}}_i}=1531.9$ The signal of nanometer and idle photon are to resulting from the optical fiber 8.When along clockwise and the photon of counterclockwise propagating in 7 couplings of 50/50 beam splitter, not only the polarization direction is identical, and two bundle pump light phase shifts of transmission in opposite directions are when being n π (n is an integer), the output state of Sagnac fiber optic loop is Rather than

Fig. 6 (b) and (c) be the frequency spectrum of wave filter 15 at flashlight and idle optical channel can see that their centre wavelength is respectively 1544.5 nanometers and 1531.9 nanometers, and further these two passages of test specification to the isolation of pump photon greater than 100dB.

The optical fiber polarization controller 13 of adjusting Fig. 6 (a) middle port 2 ' makes the scattered photon parallel with pump light by behind the polarization beam apparatus 13, again by bandpass filter 15 output signal photons and idle photon, and measure with single- photon detector 23 and 24 respectively, detector 23 and 24 output signal are imported computer-controlled single photon data acquisition system (DAS) 25, analyze and write down the single channel counting and the coincidence counting of two detectors.Fig. 6 (d) is the average power of input pumping light when changing, and produces the coincidence counting of photon and the result of the coincidence counting at random calculated according to the single channel counting by same pulse.From Fig. 6 (d) as can be known, coincidence counting and coincidence counting is basic identical at random, illustrate that no quantum is related between the signal photon measured and idle photon, the signal and the idle photon of the same port output of Sagnac fiber optic loop this moment are not right by the photon of same pulse generation, and promptly Shu Chu state is not

Next, we observe the signal of the different output ports of Sagnac fiber optic loop and the related situation of idle photon again.Experimental provision as shown in Figure 7.After the difference of Fig. 7 and Fig. 6 was that the optical fiber polarization controller 13 of port 2 ' can make that the scattered photon parallel with pump light by polarization beam apparatus 14 passes through, 15 of bandpass filter were selected signal photon (1544.5 nanometer) again; And port one ' optical fiber polarization controller 21 make and pass through by polarization beam apparatus 22 scattered photon parallel with pump light, select idle photon by 16 of bandpass filter again; Measure the signal photon and the idle photon of wave filter 15 and 16 outputs then with single-photon detector 23 and 24 respectively, and count and coincidence counting with the single channel of single photon data acquisition system (DAS) 25 records and analysis detector 23 and 24.The frequency spectrum of bandpass filter 16 is identical with 15, and the centre wavelength of its idle optical channel also is 1531.9 nanometers.From Fig. 7 (b) as can be known, coincidence counting is much larger than coincidence counting at random, embodied the signal photon of two port outputs and the quantum association between the idle photon, illustrated that the signal of Sagnac fiber optic loop different port output and idle photon are right by the photon of same pulse generation, promptly Shu Chu state is

Embodiment 3: the beat frequency quantum interference that the frequency entangled photons is right

As shown in Figure 8, in the all-optical frequency entangled device, adjust the optical fiber polarization controller 13 of Sagnac fiber optic loop port 2 ', make the parallel of the polarization of the scattered photon by polarization beam apparatus 14 and pump light, adjust port one simultaneously ' optical fiber polarization controller 21, make the parallel of the polarization of the scattered photon by polarization beam apparatus 22 and pump light; After will carrying out route matching by the photon of polarization beam apparatus 14 and 22 respectively then, import two input ports, wherein port ones of 50/50 fiber optic splitter 26 ' time-delay mechanism 28 and the Polarization Controller 27 of photon through constituting by catoptron and accurate translation stage of output; Two delivery outlets with 50/50 fiber optic splitter 26 pass through bandpass filter 15 and 16 respectively again, the signal photon of bandpass filter 15 and the idle photon of bandpass filter 16 are surveyed with single-photon detector 23 and 24 respectively, and measure accurate translation stage position not simultaneously, the coincidence counting of two single photon devices and single channel counting.Measurement result shows that single channel is counted not with the translation stage change in location, and the relation of coincidence counting peace pan position demonstrates the beat frequency interference phenomenon, [annotates 2] as shown in Figure 9.Square among the figure is an experimental data, and solid line is with the relevant real data of device and to interfere contrast be the best theoretical fitting of parameter, and the result shows and interferes contrast greater than 90%, illustrates that institute of the present invention output photon is a high-purity frequency entangled photons.

List of references:

1.J.Chen，K.F.Lee，and?P.Kumar，Phys.Rev.A76，031804(R)(2007).

2.X.Li L.Yang and L.Cui will throw Phys.Rev.A

3.P.Kumar，M.Fiorentino，P.L.Voss，and?J.E.Sharping，U.S.Patent?No.6,897,434?(2005)

Claims (4)

1, a kind of all-optical frequency entangled photon source is characterized in that this photon source comprises successively:

Pump light light source: be used to produce pump light;

95/5 beam splitter: be used for 95% pump light is imported the Sagnac fiber optic loop, the pump light with 5% monitors pump power;

The Sagnac fiber optic loop: be made of circulator, 50/.50 beam splitter, optical fiber and first optical fiber polarization controller successively, wherein, circulator is used for the photon output with the reflection of Sagnac fiber optic loop; 50/50 beam splitter be used to separate pump light and to the photon of transmission in opposite directions to being coupled; It is right that optical fiber is used to produce the twin photon of quantum association; First optical fiber polarization controller is used for the compensated optical fiber birefringence and introduces phase shift;

90/10 beam splitter: be used for injecting reference signal light and output scattered photon to the Sagnac fiber optic loop;

The 3rd optical fiber polarization controller: be connected with 90% end of 90/10 beam splitter, be used to adjust polarization via 90/10 beam splitter output photon;

First fibre optic polarizing beam splitter: be connected with the 3rd optical fiber polarization controller, be used to select the polarization of output photon;

First flashlight, idle light and pump light bandpass filter: be connected with first fibre optic polarizing beam splitter, the signal that is used for being produced by spontaneous four-wave mixing in the optical fiber separates with pump light with idle photon, the light output that selection is consistent with flashlight and idle light center frequency;

The 4th optical fiber polarization controller: be connected with the circulator in the Sagnac fiber optic loop, be used to adjust the polarization of the photon of the Sagnac fiber optic loop reflection of exporting by circulator;

Second fibre optic polarizing beam splitter: be connected with the 4th optical fiber polarization controller, be used to select the polarization of output photon;

Secondary signal light, idle light and pump light bandpass filter: be connected with second fibre optic polarizing beam splitter, the signal that is used for being produced by spontaneous four-wave mixing in the optical fiber separates with pump light with idle photon, the light output that selection is consistent with flashlight and idle light center frequency.

2, entangled photons according to claim 1 source is characterized in that fiber selection zero dispersion shift fiber or microstructured optical fibers in the described Sagnac fiber optic loop, and the twin photon that is used to produce the quantum association is right; It is right that the spontaneous four-wave mixing process simultaneously scattering of the pump photon that two centre frequencies are ω p by zero dispersion shift fiber or microstructured optical fibers is that frequency is respectively flashlight and the twin photon of idle light of ω s and ω i, wherein 2 ω _p=ω _s+ ω _i, this parametric process satisfies energy conservation and momentum conservation condition.

3, entangled photons according to claim 1 and 2 source is characterized in that the composition of described pump light light source comprises successively:

Optical fiber femtosecond laser: be used for output laser pulse;

The first pump light bandpass filter: connect optical fiber femtosecond laser, adopt the light of transmission port output, to eliminate the frequency that comprised in the pumping laser photon at ω s and ω i wave band;

Fiber amplifier: be connected with the first pump light bandpass filter transmission port, be used to amplify the power of the laser pulse of first pump light bandpass filter transmission port output;

The second pump light bandpass filter: be connected with fiber amplifier, be used for eliminating wavelength that pumping laser comprises photon, and the pumping laser of transmission end output is input to 95/5 beam splitter at ω s and ω i wave band.

4, entangled photons according to claim 1 and 2 source is characterized in that this entangled photons source also comprises a reference signal radiant that is used to produce the Adjustment System parameter, and its composition comprises successively:

Optical fiber femtosecond laser: be used for output laser pulse;

The first pump light bandpass filter: connect optical fiber femtosecond laser, the output of its reflector port is used to extract frequency not at the photon of pump light centre frequency ω p wave band;

The flashlight bandpass filter: be connected with the first pump light bandpass filter reflector port, be used to extract frequency at the light of ω i wave band as the reference flashlight;

Second optical fiber polarization controller: be connected with 10% end of 90/10 beam splitter, be used to adjust the reference signal polarisation of light that injects 90/10 beam splitter.

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