Quantum information processing using linear optics

Transcription

1 Quantum information processing using linear optics Karel Lemr Joint Laboratory of Optics of Palacký University and Institute of Physics of Academy of Sciences of the Czech Republic web: Karel Lemr QIP in Olomouc 1 / 24

2 Where am I from? Karel Lemr QIP in Olomouc 2 / 24

3 Where am I from? UK France Germany Poland Spain Karel Lemr QIP in Olomouc 3 / 24

4 Where am I from? Karel Lemr QIP in Olomouc 4 / 24

5 Contents 1 Quantum information processing 2 Quantum information processing with light 3 Photon source and detection 4 Experimental toolbox 5 Recent experiments Karel Lemr QIP in Olomouc 5 / 24

6 Contents Quantum information processing 1 Quantum information processing 2 Quantum information processing with light 3 Photon source and detection 4 Experimental toolbox 5 Recent experiments Karel Lemr QIP in Olomouc 6 / 24

7 Quantum information processing Quantum information processing Quantum information processing is a collection of algorithms used to process the information using quantum laws of nature. The information can be carried by quantum states of various media (eg. light, atoms, ions) Manipulation with these carriers allows us to process the information. example: quantum cryptography, quantum gates (XOR, CNOT, CPHASE) advantages: faster algorithms, secure communication, easier numerical simulations the ultimate goal: quantum computer Karel Lemr QIP in Olomouc 7 / 24

8 Qubit Quantum information processing Qubit is the unit of quantum information. Classical bit: 0 or 1 Qubit: any superposition of 0 and 1 Eg. energy levels 0 (ground), 1 (excited) Karel Lemr QIP in Olomouc 8 / 24

9 Contents Quantum information processing with light 1 Quantum information processing 2 Quantum information processing with light 3 Photon source and detection 4 Experimental toolbox 5 Recent experiments Karel Lemr QIP in Olomouc 9 / 24

10 QIP with light Quantum information processing with light Quantum states of light are used to carry the information. Interference and subsequent measurements are used to process the information. Two approaches: continuous variables (strong beam, collective state) discrete variables (discrete photons, individual states) We use discrete photons in our experiments. Karel Lemr QIP in Olomouc 10 / 24

11 Quantum information processing with light Single photon quantum state The information is encoded into polarization and/or spatial mode. Karel Lemr QIP in Olomouc 11 / 24

12 Quantum information processing with light Discrete photon interference Single photon interference: output selected by the photon depends on the phase in the interferometer photon may exit the interferometer being in superposition of both exit outputs Karel Lemr QIP in Olomouc 12 / 24

13 Quantum information processing with light Discrete photon interference Two photon interference (Hong-Ou-Mandel): photons exit always together (by the same output) - bunching 50:50 chance of selecting one or other output Karel Lemr QIP in Olomouc 13 / 24

14 Contents Photon source and detection 1 Quantum information processing 2 Quantum information processing with light 3 Photon source and detection 4 Experimental toolbox 5 Recent experiments Karel Lemr QIP in Olomouc 14 / 24

15 Photon source and detection Spontaneous parametric down-conversion non-linear process: photon ω P 2 photons ω S, ω I special crystals (BBO, LiIO 3, KTP) manifest this non-linear behaviour pumped with laser beam non-linear crystal Single photons fiber coupling pumping beam Karel Lemr QIP in Olomouc 15 / 24

16 Photon source and detection Detection of single photons APD detectors, typical rate photons/s at the end of setup multiple detectors, post-selection of coincidences (two photons detected within 1 ns by 2 different detectors) several series of measurements allow us to perform quantum state tomography (determine the state of photons) Karel Lemr QIP in Olomouc 16 / 24

17 Contents Experimental toolbox 1 Quantum information processing 2 Quantum information processing with light 3 Photon source and detection 4 Experimental toolbox 5 Recent experiments Karel Lemr QIP in Olomouc 17 / 24

18 Beam splitters: Experimental toolbox Ordinary beam splitter: Polarizing beam splitter: mixing 2 input and output modes mixing/splitting polarization modes Karel Lemr QIP in Olomouc 18 / 24

19 Other tools: Experimental toolbox Wave plates (HWP, QWP): HWP: introduces λ 2 phase shift between two orthogonal polarizations QWP: introduces λ 4 phase shift between two orthogonal polarizations Neutral density filters for attenuation Karel Lemr QIP in Olomouc 19 / 24

20 Contents Recent experiments 1 Quantum information processing 2 Quantum information processing with light 3 Photon source and detection 4 Experimental toolbox 5 Recent experiments Karel Lemr QIP in Olomouc 20 / 24

21 Recent experiments Quantum state engineering Experimental preparation of Knill-Laflamme-Milburn states : HWP BBO single-mode fiber 4.53 MT 2 1 piezo BS1 APD APD PBS QWP HWP BS2 QWP single-mode fiber 1 HWP 2 QWP HWP PBS APD APD (a) source of entangled photon pairs (b) KLM state preparation (c) KLM state analysis special class of quantum states useful for QIP Phys. Rev. A 81, (2010) Karel Lemr QIP in Olomouc 21 / 24

22 Quantum gate Recent experiments Tunable optimal c-phase gate: MT1 1 HWP PBS1 QWP HWP 2 BDA2 F21 QWP BDA1 F22 HWP21 HWP11 piezo MT2 D1V HWP22 PBS2 HWP12 D2V F1 HWP QWP QWP HWP PBS PBS D1H D2H BDA = BD BD HWP@45deg piezo two photon QIP logic gate to be published Karel Lemr QIP in Olomouc 22 / 24

23 Setup photo Recent experiments Karel Lemr QIP in Olomouc 23 / 24

24 The end Recent experiments Thank you for your attention. This presentation is supported by the EU funds and the Ministry of Education of the Czech Republic under the project No. CZ.1.07/2.3.00/ Karel Lemr QIP in Olomouc 24 / 24