A kind of superconducting nano-wire single-photon detector and preparation method of ability resolved light subnumber
Technical field
The invention belongs to the single photon detection field, be applicable at visible light and infrared band and need realize the single photon detection that photon number is differentiated, relate to a kind of superconducting nano-wire single-photon detector and preparation method of ability resolved light subnumber.
Background technology
In recent years, the optical imagery that formerly advances of single-photon detecting survey technology, spectroscopy, high-energy physics, ultrafast Aerospace Satellite communication, radiation are surveyed and there are demand and application widely in fields such as quantum information.G.N.Gol ' tsman et al.; " Picosecond superconducting single-photon optical detector; " Applied Physics Letter; Vol.79; Pp.705-707, the superconducting nano-wire single-photon detector (SNSPD) of 2001. records rises since its birth, owing to its single photon detection ability in visible light and infrared band excellence, superelevation counting rate, low dark counts, very little time jitter extensively receive people's attention; Especially its quantum efficiency and the peak count rate that can realize at near-infrared band has all surpassed existing avalanche diode based on composite semiconductor material, makes it become the strongest candidate's detectors in field such as quantum communication.But, comprise that nearly all single-photon detector of traditional SNSPD is operated in very strong nonlinear model, make that its reaction and incident light subnumber to incident photon is irrelevant, promptly can't differentiate the photon number of incident simultaneously.For SNSPD also can satisfy simultaneously the demand (such as the characteristic present of linear optics quantum calculation, quantum repeater, non-classical light source etc.) of the special applications that some needs photon number differentiates, we need do some improvement to traditional SNSPD.People have proposed two kinds of different schemes at present, can be so that SNSPD has photon number resolution characteristic: US7,638; 751B2 " Multi-element optical detectors with sub-wavelength gaps " E.A.Dauler; A.J.Kerman, K.K.Berggren, V.Anant; SNSPD array and RU 2346357C1 " Superconducting photon-counting detector for visible and infrared spectral range " G.N.Gol ' tsman that J.K.W.Yang etc. propose; G.M.Chulkova, A.A.Korneev, the parallelly connected nano wire detector (PND) that A.V.Divochij etc. propose.But the SNSPD array needs a very huge and complicated sensing circuit, because its each SNSPD unit needs independent amplifier, biasing circuit and Discr. respectively.Though PND does not need so complicated sensing circuit, leakage current becomes its fatal hard defects, seriously limits its quantum efficiency and the highest distinguishable photon number.
Summary of the invention
In order to overcome the deficiency of above-mentioned prior art; The object of the present invention is to provide a kind of superconducting nano-wire single-photon detector and preparation method of ability resolved light subnumber; Its quantum efficiency is high, counting rate is high, dark counts is low, have the photon number resolution characteristic, and does not receive influence of leakage current.
To achieve these goals, the technical scheme of the present invention's employing is:
A kind of superconducting nano-wire single-photon detector of ability resolved light subnumber is made up of the superconducting nano-wire and a corresponding N bypass resistance of N series connection.
Said each bypass resistance is arranged between per two adjacent superconducting nano-wires.
Said N is the integer more than or equal to 2, such as 4,6,8 etc.
Said superconducting nano-wire is that superconductors such as niobium nitride or niobium nitride titanium are processed, and bypass resistance is processed by metallic films such as gold or titaniums.
The present invention also provides a kind of method for preparing the superconducting nano-wire single-photon detector of said ability resolved light subnumber, may further comprise the steps:
The first step, growth of superconductive film on the sapphire of twin polishing or MgO substrate, film thickness is at 2~8nm;
Second step, the nano wire figure of design serpentine structure, spin coating electron sensitive resist on film then; Expose required graphical window with electron beam exposure apparatus again; Obtain the figure that designed through reactive ion etching at last, nanowire width is between 50-100nm, and dutycycle is 30~60%;
The 3rd step, on existing nano thread structure, step such as proceed spin coating electron sensitive resist, electron beam alignment, metallic film deposit, peel off, the electrode of making resistance on the sheet and being connected in the device two ends is used to derive signal.
Film thickness is preferably between 4~6nm in the said first step.
The integral body that nano wire covers in said second step is square, and its length of side is preferably 10 μ m.
Dutycycle is preferably in about 50% in said second step.
The present invention compared with prior art has the characteristics of high-quantum efficiency, high count rate and low dark counts, has the photon number resolution characteristic simultaneously, and does not receive influence of leakage current.
Description of drawings
Fig. 1 is the device architecture synoptic diagram of 4-SND;
Fig. 2 is a superconducting single-photon detection system structural representation;
Fig. 3-5 is the equivalent circuit theory figure of N-SND;
Fig. 6-8 is the electric heating simulation result of 6-SND.
Embodiment
Below in conjunction with accompanying drawing and embodiment the present invention is explained further details.
As shown in Figure 1; Superconducting nano-wire single-photon detector for a kind of ability resolved light subnumber; Superconducting nano-wire and corresponding 4 bypass resistances by 4 series connection are formed; Be provided with a bypass resistance between every two adjacent superconducting nano-wires, superconducting nano-wire is that niobium nitride is processed, and bypass resistance is processed by gold thin film.The principle of work of each unit and traditional SNSPD are basic identical, all are based on storehouse uncle that the absorption of photon causes to destroying and heat island (hotspot) generation principle.
As shown in Figure 2; Each section superconducting nano-wire can equivalence become an inductance and a variable resistor in the device; Wherein inductance value is determined by the size of the dynamic inductance of corresponding that section nano wire, and variable resistance is represented the size (variable resistance is not zero when having photon incident) of heat island resistance.During work, device current is biased in the place that is in close proximity to critical current, like 0.95Ic; Because each nano wire all is connected in series; So all nano wires all are biased on the onesize electric current, and because all nano wires all are in superconducting state when not having photon incident, all bias currents only can pass through nano wire; Be bypass resistance all by short circuit, this moment, device two ends output voltage was zero.
As n (1≤n≤when N) individual photon incides different nano wire region respectively; N heat island is formed respectively; Then the subregion quench of n nano wire has a resistance, and a big chunk electric current that causes originally flowing through through nano wire is compelled to flow to corresponding bypass resistance; As shown in Figure 3, the input impedance R of expression low temperature amplifier
OutMuch larger than bypass resistance R
Sh, and R
ShSituation during again much smaller than heat island resistance.
There is not the nano wire of photon incident then to continue to keep superconducting state, so corresponding bypass resistance also continues to keep by short circuit.If, can expect that obtaining one highly is about n * (I with the voltage signal at the voltage amplifier reading device two ends of high input impedance
Bias-I
Return) * R
Sh* A is the fast-pulse of direct ratio and n, wherein I
BiasBe bias current value, I
ReturnBe nano wire electric current through nano wire when normal state is got back to superconducting state, A then is the total magnification of two amplifiers.
As shown in Figure 4, because the flow direction of transient current and bias current just in time are opposite,, rather than increase so process does not have the electric current of the nano wire of photon incident temporarily slightly to reduce.
Fig. 5-7 is depicted as the electric heating simulation result that a 6-SND obtains under the condition of 2K temperature and 95% bias current.The bypass resistance that this 6-SND is wide by 6 100nm, 4nm thin, the NbN nano wire of 50% dutycycle and 6 resistances are 50 Ω is formed, and the total useful detection area of device is 12 * 12 μ m
2, in addition, the input impedance of low temperature amplifier is set at 1K Ω.Can see that from Fig. 5 under different n value conditions (being the different incident photon number), available pulse height is direct ratio and the photon number that detects well.Therefore; Can from the pulse height resolved detection after amplifying to photon number; And because the resume speed of nano wire bias current does not significantly concern with incident light subnumber n; Like Fig. 6, when n photon electric current through the nano wire that absorbs photon when surveying develops in time, therefore can not lose the quantity N that continues to increase the series connection nano wire under the situation of peak count rate and improve the highest distinguishable photon number.Fig. 7 can see that electric current can have decline slightly earlier along with the time, and then turn back to initial value for pass through the electric current evolution in time of the nano wire that does not have photon incident when surveying when n photon from scheme.Like this; SND takes place with regard to the situation that can might not cause the nano wire mistake upset that does not have photon incident as PND has the instantaneous increase of the sort of electric current; It is the influence that SND does not receive leakage current fully; Then can be operated under the condition that bias current is in close proximity to its critical current, quantum efficiency can be significantly improved, and the quantity N of series connection nano wire also can be set in bigger value.
As shown in Figure 8, except being used to survey the superconductive device of incident photon signal, constitute also needs of whole detection system:
(1) can cool to the refrigeration machine of 2-4K: low temperature environment is provided to superconductive device;
(2) low-noise current source: the DC current biasing is provided to superconductive device;
(3) the low temperature RF amplifier of special high input impedance and commercial low noise room temperature RF amplifier: be used for the two-stage amplification and read ultrafast voltage pulse signal, connect with concentric cable between two amplifiers;
(4) sheet upper offset tree (bias-T): current source is received the dc terminal of biasing tree, and the radio-frequency head of biasing tree is directly received on the low temperature amp.in, and the other end of biasing tree is directly received on the device electrode;
(5) counter and high-speed oscilloscope: the pulse signal of reading is counted and wave form analysis;
(6) light path system: be used for coupling, transmission and regulate incident optical signal, form by light source, adjustable light power attenuator, adjustable polarizer, fiber coupler, optical fiber, light power meter and micro positioner.