Verification of Rydberg level assisted light shift imbalance induced blockade in an atomic ensemble

Transcription

1 Verification of Rydberg level assisted light shift imbalance induced blockade in an atomic ensemble May E Kim Yanfei Tu Subramanian Krishnamurthy Selim Shahriar Northwestern U

2 Questions to answer How can an atom be used in quantum computing? What is the advantage of using an ensemble of atoms as opposed to one? How can the ensemble states be controlled and manipulated using dipole dipole interaction and light shift? What is the experimental setup for verifying the theory?

3 Requirements for quantum computing general Closed box - storage (Relatively) fast gate operation - dynamics Open box - measurement qubit qubit qubit qubit Random processes

4 Requirements for quantum computing single atom Closed box - storage (Relatively) fast gate operation - dynamics Open box - measurement Interaction with light Florescence detection Long lived hyperfine ground states

5 Requirements for quantum computing Atomic ensemble Advantages: No need to isolate a single atom Long lived (hyperfine ground) states Interaction with light Enhancement in interaction strength Potentially couple to longer optical cavity (Pelizzari scheme) Single photon source on demand Challenge: Equal energy separation Need to control the interaction

6 Light shift imbalance induced blockade (1) One atom Lower levels have same energy separation Interaction with light will shift energy levels Large detuning: Right choices of laser intensity: Two atoms Shahriar, M. S. et al. Light-shift imbalance induced blockade of collective excitations beyond the lowest order, Optics Comm. 278, (2007).

7 Light shift imbalance induced blockade (2) One atom N atoms Two atoms Shahriar, M. S. et al. Light-shift imbalance induced blockade of collective excitations beyond the lowest order, Optics Comm. 278, (2007).

8 Collective excitation Hamiltonian Hamiltonian in the product states: Hamiltonian after rotation by 45: Collective state description New finding: Collective states are simply product states: puts constraints on dealing with semi-classical collective states.

9 Collective excitation Summary Collective states evolve as the product of two independent states: In product states, coefficients are dependent: Dipole dipole interaction is needed to entangle the atoms.

10 Rydberg states (1) Rydberg states are highly excited states: Two-body interaction strength for ground-state Rb atoms, Rb atoms excited to the 100s level, and ions: Saffman, Mark, T. G. Walker, and Klaus Mølmer. "Quantum information with Rydberg atoms." Reviews of modern Physics 82.3 (2010): 2313.

11 Rydberg states (2)

12 Rydberg + LSIB simulation result (1) Simplified picture (1 atom) Evolution in time of the population in different states (NO dipole dipole interaction) Simplified picture (2 atoms)

13 Rydberg + LSIB simulation result (2) Simplified picture (1 atom) Evolution in time of the population in different states (WITH dipole dipole interaction) Simplified picture (2 atoms)

14 Summery/Reminder Why use ensemble states? Strongly interacting system (fast gate operations) Alternative: single atoms (small cavities) What s the blockade for? Control and manipulation of ensemble states Produce entanglement How is this useful? Quantum logic gate operations Single photon source on demand

15 Verification of LSIB (1) 2 1 Verify that the population oscillates between G 2,1 > and Actual states (Rb 87 D2): G 2 > 2 ( N 1) G 1, 2 > 1 2 G 1, 1 > 3 2 N 1 G 1 > 2 ( N 1) ( N 2) C 2 > 1 C 3 > C 1 > A> Initialization: MOT Dipole trap Show that only a single photon is produced by the system Experiment

16 Verification of LSIB (2) Step 1 (pi pulse): Step 2 (pi pulse): Single photon detected

17 Verification of LSIB (3) Dudin, Y. O., and A. Kuzmich. "Strongly interacting Rydberg excitations of a cold atomic gas." Science (2012): Hansbury Brown and Twiss detection setup Coincidence measurement 2nd order correlation function at zero delay If measured values are below unity, only one photon excitation : probability for D1 : probability for D2 : probability for double coincidence Accomplish: Verification of blockade (entanglement) Single photon source on demand

18 Verification of LSIB (4)

19 Laboratory for Atomic and Photonic Technology Northwestern University Left to right: Mohamed Fouda Ye Wang Subramanian Krishnamurthy Shih Tseng Zifan Zhou Yanfei Tu Ren Peng Fang May Kim Joshua Yablon Selim Shahriar Jacob Scheuer Mehjabin Monjur Resham Sarkar Not pictured: Selam Nida Visiting scientists: Tony Abi-Salloum Alex Heifetz Philip Hemmer Gour Pati Renu Tripathi