Seminars & Lectures
| * TITLE | Protecting Quantum Information from Decoherence using Weak Measurement & Scheme for Directly Observing the Noncommutativity of the Position and Momentum Operators with Interference | ||||||
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| * DATE / TIME | 2014-05-20, 16:00 | ||||||
| * ABSTRACT | |||||||
| Protecting Quantum Information from Decoherence using Weak Measurement: Decoherence, often caused by unavoidable coupling with the environment, leads to degradation of quantum coherence. For a multipartite quantum system, decoherence leads to degradation of entanglement and, in certain cases, entanglement sudden death. Tackling decoherence, thus, is a critical issue faced in quantum information, as entanglement is a vital resource for many quantum information applications including quantum computing, quantum cryptography, quantum teleportation, and quantum metrology. In this talk, I will show our recent proposal and demonstration of a novel scheme to protect qubits from decoherence [1,2]. The new qubit protection scheme makes use of the quantum measurement itself for actively battling against decoherence and it can effectively circumvent even entanglement sudden death. The scheme is based on the fact that weak quantum measurement can be reversed. The reversibility of weak quantum measurement was originally discussed in the context of quantum error correction and was demonstrated for a single-superconducting qubit and a single-photonic qubit [3]. In the scheme, a weak measurement before the decoherence changes the state to a state closer to the ground state, where decoherence is minimized, and the reversing measurement recovers original state after the decoherence. The decoherence suppression scheme is implemented in photonic polarization qubits [1,2]. Our weak measurement-based scheme effectively suppress amplitude damping decoherence for a single-qubit [2]. Also, for the two-qubit system where entanglement is involved, the scheme can reduce or even completely nullify the effect of decoherence as evidenced in increased concurrence of the two-qubit system [1]. The new entanglement protection protocol can indeed be useful for battling against decoherence. In particular, for amplitude damping decoherence, it is shown that the protocol can distribute (protect) entanglement even through (from) severe decoherence. The trade-off relation between the success probability, concurrence, and weak measurement strength is also studied [1]. While the demonstration in this work was done for two-photon polarization qubits, the protocol can easily be applied to other types of qubits, making weak measurement and quantum measurement reversal powerful tools for battling against decoherence. References [1]Y.-S. Kim, J.-C. Lee, O. Kwon, and Y.-H. Kim, Nature Phys. 8, 117 (2012). [2]J.-C. Lee, Y.-C. Jeong, Y.-S. Kim, and Y.-H. Kim, Opt. Express 19, 16309 (2011). [3]Y.-S. Kim, Y.-W. Cho, Y.-S. Ra, and Y.-H. Kim, Opt. Express 17, 11978 (2009). ---------------------------------------------------------------------------------------------- Scheme for Directly Observing the Noncommutativity of the Position and Momentum Operators with Interference: The noncommutativity of complementary observables is the ground for many unique quantum effects, as well being the active subject of many illuminating debates on quantum physics. Yet, although the commutation relation has been well established theoretically since Heisenberg introduced the canonical commutation relation of the position and the momentum operators, experimental tests on the noncommutativity of conjugate operators have been rather limited. The noncommutativity of photonic Pauli spin operators has been demonstrated [1]. Also, the noncommutativity of bosonic creation and annihilation operators has recently been demonstrated with photons [2]. However, the noncommutativity between the position and the momentum operators has always been associated with the uncertainty principle and, in experiment, it has been demonstrated in single-slit diffraction [3]. Note that the noncommutativity relation for the position and the momentum operators itself has not been directly observed to date unlike the Pauli spin operators or the bosonic creation and annihilation operators. We propose and analyze an experimental scheme to directly observe the noncommutativity of the position and the momentum operators using the transverse spatial degree of freedom x of a single-photon wave function ψ(x) [in the sense that |ψ(x)|2 gives the probability distribution] [4]. Although the interferometric scheme proposed in this paper is focused on single-photon interferometry, the proposed concept can readily be expanded to matter-wave interferometry. References [1] Y.-S. Kim, H.-T. Lim, Y.-S. Ra, and Y.-H. Kim, “Experimental verification of the commutation relation for Pauli spin operators using single-photon quantum interference,” Phys. Lett. A, vol. 374, pp. 4393, 2010. [2] A. Zavatta, V. Parigi, M. S. Kim, H. Jeong, and M. Bellini, “Experimental Demonstration of the Bosonic Commutation Relation via Superpositions of Quantum Operations on Thermal Light Fields,” Phys. Rev. Lett., vol. 103, pp. 140406, 2009. [3] C. G. Shull, “Single-Slit Diffraction of Neutrons,” Phys. Rev., vol. 179, pp. 752, 1969. [4] J.-C. Lee, Y.-S. Kim, Y.-S. Ra, H.-T. Lim, and Y.-H. Kim, “Scheme for directly observing the noncommutativity of the position and the momentum operators with interference,” Phys. Rev. A, vol. 86, pp. 042112, 2012. |
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| * ABSTRACT FILE | APCTP_Abstract2.pdf | ||||||
