Mark Um
Tsinghua University
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Publication
Featured researches published by Mark Um.
Nature Physics | 2015
Shuoming An; Jing-Ning Zhang; Mark Um; Dingshun Lv; Yao Lu; Junhua Zhang; Zhang-qi Yin; H. T. Quan; Kihwan Kim
The Jarzynski equality, relating non-equilibrium processes to free-energy differences between equilibrium states, has been verified in a number of classical systems. An ion-trap experiment now succeeds in demonstrating its quantum counterpart.
Physical Review Letters | 2013
X. P. Zhang; Mark Um; Junhua Zhang; Shuoming An; Ye Wang; Dong-Ling Deng; Chao Shen; L. M. Duan; Kihwan Kim
Using a single trapped ion, we have experimentally demonstrated state-independent violation of a recent version of the Kochen-Specker inequality in a three-level system (qutrit) that is intrinsically indivisible. Three ground states of the (171)Yb(+) ion representing a qutrit are manipulated with high fidelity through microwaves and detected with high efficiency through a two-step quantum jump technique. Qutrits constitute the most fundamental system to show quantum contextuality and our experiment represents the first one that closes the detection efficiency loophole for experimental tests of quantum contextuality in such a system.
Scientific Reports | 2013
Mark Um; X. P. Zhang; Junhua Zhang; Ye Wang; Shen Yangchao; Dong-Ling Deng; L. M. Duan; Kihwan Kim
The intrinsic unpredictability of measurements in quantum mechanics can be used to produce genuine randomness. Here, we demonstrate a random number generator where the randomness is certified by quantum contextuality in connection with the Kochen-Specker theorem. In particular, we generate random numbers from measurements on a single trapped ion with three internal levels, and certify the generated randomness by showing a bound on the minimum entropy through observation of violation of the Klyachko-Can-Binicioglu-Shumovsky (KCBS) inequality. Concerning the test of the KCBS inequality, we close the detection efficiency loophole for the first time and make it relatively immune to the compatibility loophole. In our experiment, we generate 1 × 105 random numbers that are guaranteed to have 5.2 × 104 bits of minimum entropy with a 99% confidence level.
Nature Communications | 2016
Mark Um; Junhua Zhang; Dingshun Lv; Yao Lu; Shuoming An; Jing-Ning Zhang; Hyunchul Nha; M. S. Kim; Kihwan Kim
Single-quantum level operations are important tools to manipulate a quantum state. Annihilation or creation of single particles translates a quantum state to another by adding or subtracting a particle, depending on how many are already in the given state. The operations are probabilistic and the success rate has yet been low in their experimental realization. Here we experimentally demonstrate (near) deterministic addition and subtraction of a bosonic particle, in particular a phonon of ionic motion in a harmonic potential. We realize the operations by coupling phonons to an auxiliary two-level system and applying transitionless adiabatic passage. We show handy repetition of the operations on various initial states and demonstrate by the reconstruction of the density matrices that the operations preserve coherences. We observe the transformation of a classical state to a highly non-classical one and a Gaussian state to a non-Gaussian one by applying a sequence of operations deterministically.Mark Um, Junhua Zhang, Dingshun Lv, Yao Lu, Shuoming An, Jing-Ning Zhang, Hyunchul Nha, M. S. Kim4∗ and Kihwan Kim1† Center for Quantum Information, Institute for Interdisciplinary Information Sciences, Tsinghua University, Beijing 100084, P. R. China School of Computational Sciences, Korea Institute for Advanced Study, Seoul 130-722, Korea Texas A&M University at Qatar, Education City, P.O. Box 23874, Doha, Qatar QOLS, Blackett Laboratory, Imperial College London, SW7 2AZ, United Kingdom
Nature Photonics | 2017
Ye Wang; Mark Um; Junhua Zhang; Shuoming An; Ming Lyu; Jing Ning Zhang; L. M. Duan; Dahyun Yum; Kihwan Kim
A long-time quantum memory capable of storing and measuring quantum information at the single-qubit level is an essential ingredient for practical quantum computation and communication1,2. Currently, the coherence time of a single qubit is limited to less than 1 min, as demonstrated in trapped ion systems3–5, although much longer coherence times have been reported in ensembles of trapped ions6,7 and nuclear spins of ionized donors8,9. Here, we report the observation of a coherence time of over 10 min for a single qubit in a 171Yb+ ion sympathetically cooled by a 138Ba+ ion in the same Paul trap, which eliminates the problem of qubit-detection inefficiency from heating of the qubit ion10,11. We also apply a few thousand dynamical decoupling pulses to suppress ambient noise from magnetic-field fluctuations and phase noise from the local oscillator8,9,12–16. The long-time quantum memory of the single trapped ion qubit would be the essential component of scalable quantum computers1,17,18, quantum networks2,19,20 and quantum money21,22.The longest coherence time of a single qubit of more than ten minutes is observed in a 171Yb+ ion. After sympathetically cooling the 171Yb+ ion qubit with a 138Ba+ ion, noise from magnetic-field fluctuations and the local oscillator is suppressed by a dynamic decoupling scheme.
Physical Review Letters | 2015
Jiyong Park; Junhua Zhang; Jaehak Lee; Se-Wan Ji; Mark Um; Dingshun Lv; Kihwan Kim; Hyunchul Nha
We theoretically propose and experimentally demonstrate a nonclassicality test of a single-mode field in phase space, which has an analogy with the nonlocality test proposed by Banaszek and Wódkiewicz [Phys. Rev. Lett. 82, 2009 (1999)]. Our approach to deriving the classical bound draws on the fact that the Wigner function of a coherent state is a product of two independent distributions as if the orthogonal quadratures (position and momentum) in phase space behave as local realistic variables. Our method detects every pure nonclassical Gaussian state, which can also be extended to mixed states. Furthermore, it sets a bound for all Gaussian states and their mixtures, thereby providing a criterion to detect a genuine quantum non-Gaussian state. Remarkably, our phase-space approach with invariance under Gaussian unitary operations leads to an optimized test for a given non-Gaussian state. We experimentally show how this enhanced method can manifest quantum non-Gaussianity of a state by simply choosing phase-space points appropriately, which is essentially equivalent to implementing a squeezing operation on a given state.
Physical Review A | 2017
Dingshun Lv; Shuoming An; Mark Um; Junhua Zhang; Jing-Ning Zhang; M. S. Kim; Kihwan Kim
A quantum state is fully characterized by its density matrix or equivalently by its quasiprobabilities in phase space. A scheme to identify the quasiprobabilities of a quantum state is an important tool in the recent development of quantum technologies. Based on our highly efficient vacuum measurement scheme, we measure the quasiprobability
Scientific Reports | 2018
Mark Um; X. P. Zhang; Junhua Zhang; Ye Wang; Yangchao Shen; Dong-Ling Deng; Lu-Ming Duan; Kihwan Kim
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arXiv: Quantum Physics | 2016
Junhua Zhang; Mark Um; Dingshun Lv; Jing-Ning Zhang; Lu-Ming Duan; Kihwan Kim
-function of the vibrational motion for a \Yb ion {\it resonantly} interacting with its internal energy states. This interaction model is known as the Jaynes-Cummings model which is one of the fundamental models in quantum electrodynamics. We apply the capability of the vacuum measurement to study the Jaynes-Cummings dynamics, where the Gaussian peak of the initial coherent state is known to bifurcate and rotate around the origin of phase space. They merge at the so-called revival time at the other side of phase space. The measured
Bulletin of the American Physical Society | 2016
Ye Wang; Dahyun Yum; Ming Lyu; Shuoming An; Mark Um; Junhua Zhang; Lu-Ming Duan; Kihwan Kim
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