1、Toward“Quantum Supremacy”with Multiphoton Boson SamplingA real quantum machine which is more powerful than early classical computers,such as ENIAC and TRADIC.Quantum information processing with photonsQuantum bits can be encoded in the polarization of single photons|0|1HV Arbitrary SU(2)rotationProj
2、ective measurementWhy do we like photons?R Flying qubit(fastest quantum information transmitter)R Robust qubit(with weak interaction with environment)R High-precision manipulation with off-the-shell devices Optical quantum computingSingle-photon sourcesUnitary transformation(beam splitters+phase shi
3、fters)Adaptive measurementsUniversal quantum computing!Single-photon sourcesUnitary transformation(beam splitters+phase shifters)Photon number measurementsNon-universal quantum computing!2-qubit gates,fault toleranceMillions of physical qubits-Tens of physical qubitsBoson Sampling for photonsCZ-gate
4、,error correction Classical Boson Boson sampling Boson sampling Boson sampling is a sampling problem;Calculating a permanent needsO(n2n)time,its a#P-complete hardproblem for classical computers.Its a feasible way to demonstratequantum supremacy.It might provide direct experimentalevidence against Ex
5、tended Church-Turing thesis.Boson sampling experimentsboson sampling tested up to 3 photons for arbitrary input configurations.Broome et al.,Science 339,794-798(2013);Spring et al.,Science 339,798-801(2013).Tillmann et al.,Nat.Photon.7,540-544(2013);Crespi et al.,Nat.Photon.7,545-549(2013).Carolan e
6、t al.,Science 349,711-716(2015);Bentivegna et al.,Science Adv.1,e1400255(2015).What are limiting us?Scott Aaronson&Alex Arkhipov,arXiv.1309.7460If we want to build a high performance boson sampling machine,we have to develop:1.perfect single-photon sources 2.large-scale ultra-low-loss photonic circu
7、it 3.high efficiency photon detectors+Single-photon sourcesRoy J.Glauber Nobel Prize 2005Indistinguishable single photonsHong-Ou-Mandel interferencefor indistinguishable photonsii“exchange interaction”Developing a perfect single-photon source1.High quantum efficiencythe decay of excited states shoul
8、d predominantly result in an emitted photon.2.Deterministic generationupon a pulsed excitation,the source should deterministically emit one photon in a push-button fashion.3.High puritythe emission should have a vanishing multi-photon probability.G2(0)=04.High indistinguishabilityindividual photons
9、emitted at different trials should be quantum mechanically identical to each other.5.High collection efficiencythe radiated photons should be extracted with a high efficiency to a single spatial mode.Checklist:A self-assembled InAs/GaAs Quantum DotInAsGaAsSelf-assembled QDs grown through MBE30nm4nme
10、lectronholeconduction bandvalence bandQuantum dot single-photon sourcesCoherent control of single photon emissionPulsed s-shell resonant excitation of a quantum dot deterministically generates single photons with near-unity indistinguishabilityY.-M.He et al.Nature Nanotechnology 8,213(2013)HOM visib
11、ility:0.97(2)Y.-J.Wei et al.Nano Letters 14,6515(2014)HOM visibility:0.99(5)Developing a perfect single-photon source1.High quantum efficiencythe decay of excited states should predominantly result in an emitted photon.2.Deterministic generationupon a pulsed excitation,the source should deterministi
12、cally emit one photon in a push-button fashion.3.High puritythe emission should have a vanishing multi-photon probability.G2(0)=04.High indistinguishabilityindividual photons emitted at different trials should be quantum mechanically identical to each other.5.High collection efficiencythe radiated p
13、hotons should be extracted with a high efficiency to a single spatial mode.Checklist:Perfect single-photon sourcesRabi oscillationCollected over 3.7 millionsingle-photon per secondSecond-order correlationg2(0)99%Spectral overlap:99.9%The first prototype photonic quantum computer(simulator)that,after
14、 20 years development,show a computational complexity that can challenge the early classical computers(ENIAC,TRADIC)Multi-photon boson sampling machineH.Wang et.al.Nature Photon.11,361(2017)H.Wang et.al.Nature Photon.11,361(2017)Multi-photon boson sampling machine Multi-photon boson sampling machine
15、The fidelity of 3-,4-and 5-boson sampling is 0.984(1),0.979(5)and 0.973(9).The sampling rate is 24000 times faster than all previous experiments,and 10-100 times faster than early classicalComputers,ENIAC and TRADIC.Y.He et.al.Phys.Rev.Lett.118,190501(2017)Time-Bin-Encoded boson sampling machineThe observed three-and four-photon boson sampling rates are 18.8 and 0.2 Hz,respectively,which are more than 100 times faster than previous experiments based on parametric down-conversion.
