1 Realization of qubit and electron entangler with NanoTechnology Emilie Dupont

2 Plan 1. Quantum computing 2. Realization of a QUantum Bit. 3. Why an electron entangler is needed ? 4. Experimental setup

3 Quantum computing Cryptography: perfectly secure communication. Searching, especially algorithmic searching Simulating quantum-mechanical systems efficiently. Efficiency: factorising a 300 digits number in 1 sec / 150,000 years for a classical computer

4 Quantum computing A. Aspect et al, PRL 49, 1804 (‘82) A. Aspect, Nature 398, 189 ('99) Quantum operator useful for factoring + security Entanglement : 1 measure instantaneously know other

5 Quantum Qubit artificial atom AlGaAs heterostructure : depleting a 2DEG inside create a quantum dot With gate : controlling the energy level of e- in the dots D. Berman, N. B. Zhitenev, and R. C. Ashoori Phys. Rev. Lett. 82, 161 (1999) van der Wiel et al Rev. Mod. Phys. 75, 1 (2003)

6 Quantum Qubit Double dots = qubit: leads on resonance + choice of gate voltage: (0,1) or (1,0) spin qubit: 1 e- out of resonance

7 Electron Entangler Superconducting lead = source of Cooper pairs Correlated e- on the dots but spatially separated = EPR pairs But noise effect É. Dupont and K. Le Hur Phys. Rev. B 73, (2006)

8 Operation on Qubit Novel entanglement mechanisms based on the prolific combination of charge and spin qubits. The spin entanglement can be controlled by the charge qubit. (Effect of charge noise will be neglected) K. Le Hur, P. Recher, É. Dupont, and D. Loss Phys. Rev. Lett. 96, (2006)

9 Measurements and Experimental setup SC + Carbon Nanotubes easier and same conclusion Samuelson, Sukhorukov, Büttiker, PRB 61, R16303 ('00) PRB 70, ('04) C. Bena, S. Vishveshawara, L. Balents, M. Fisher PRL 89, ('02) Measure of the spin state of the electron with a beam-splitter

10 Conclusion Can create an EPR pair but affected by noise. Can control spin entanglement by the state of charge qubit. Experimentaly feasible (CNT…).