Direct and full-scale experimental verifications towards ground-satellite quantum key distribution
J. –Y. Wang, B. Yang, S. –K. Liao, L. Zhang, Q. Shen, X. –F. Hu, J. –C. Wu, S. –J. Yang, Y. –L. Tang, B. Zhong, H. Liang, W. –Y. Liu, Y. –H. Hu, Y. –M. Huang, J. –G. Ren, G. –S. Pan, J. Yin, J. –J. Jia, K. Chen, C. –Z. Peng, and J. –W. Pan
Nature Photonics7 387-393， MAY 2013
Quantum key distribution (QKD) provides the only intrinsically unconditional secure method for communication based on the principle of quantum mechanics. Compared with fibre-based demonstrations, free-space links could provide the most appealing solution for communication over much larger distances. Despite significant efforts, all realizations to date rely on stationary sites. Experimental verifications are therefore extremely crucial for applications to a typical low Earth orbit satellite. To achieve direct and full-scale verifications of our set-up, we have carried out three independent experiments with a decoy-state QKD system, and overcome all conditions. The system is operated on a moving platform (using a turntable), on a floating platform (using a hot-air balloon), and with a high-loss channel to demonstrate performances under conditions of rapid motion, attitude change, vibration, random movement of satellites, and a high-loss regime. The experiments address wide ranges of all leading parameters relevant to low Earth orbit satellites. Our results pave the way towards ground–satellite QKD and a global quantum communication network.
Single-Photon-Level Quantum Image Memory Based on Cold Atomic Ensembles
Dong-Sheng Ding, Zhi-Yuan Zhou, Bao-Sen Shi, and Guang-Can Guo
Nature Communications 4, Article number: 2527(2013)
A quantum memory is a key component for quantum networks, which will enable the distribution of quantum information. Its successful development requires storage of single-photon light. Encoding photons with spatial shape through higher-dimensional states significantly increases their information-carrying capability and network capacity. However, constructing such quantum memories is challenging. Here we report the first experimental realization of a true single-photon-carrying orbital angular momentum stored via electromagnetically induced transparency in a cold atomic ensemble. Our experiments show that the non-classical pair correlation between trigger photon and retrieved photon is retained, and the spatial structure of input and retrieved photons exhibits strong similarity. More importantly, we demonstrate that single-photon coherence is preserved during storage. The ability to store spatial structure at the single-photon level opens the possibility for high-dimensional quantum memories.
Trapping red blood cells in living animals using optical tweezers
Zhong, MC (Zhong, Min-Cheng); Wei, XB (Wei, Xun-Bin); Zhou, JH (Zhou, Jin-Hua); Wang, ZQ (Wang, Zi-Qiang); Li, YM (Li, Yin-Mei)
NATURE COMMUNICATIONS 4 1768, FEB 23,2013
The recent development of non-invasive imaging techniques has enabled the visualization ofmolecular events underlying cellular processes in live cells. Although microscopic objects canbe readily manipulated at the cellular level, additional physiological insight is likely to begained by manipulation of cells in vivo, which has not been achieved so far. Here we useinfrared optical tweezers to trap and manipulate red blood cells within subdermal capillariesin living mice. We realize a non-contact micro-operation that results in the clearing of ablocked microvessel. Furthermore, we estimate the optical trap stiffness in the capillary. Ourwork expands the application of optical tweezers to the study of live cell dynamics in animals.
Sensing and atomic-scale structure analysis of single nuclear-spin clusters in diamond
Fazhan Shi, Xi Kong, Pengfei Wang, Fei Kong, Nan Zhao, Ren-Bao Liu and Jiangfeng Du
NATURE PHYSICS PUBLISHED ONLINE: 24 NOVEMBER 2013
Single-molecule nuclear magnetic resonance is a current challenge in the field of magnetic resonance spectroscopy and has important applications in chemical analysis and quantum computing. Through decoherence measurements of nitrogen– vacancy centres under dynamical decoupling control, the sensing of a single 13C nuclear spin at nanometre distance has recently been realized1–3. A further step towards the ultimate goal of structure analysis of single molecules would be the direct measurement of the interactions within single nuclearspin clusters4. Here we sense a single 13C–13C nuclear-spin dimer located about 1nm from the nitrogen–vacancy centre and characterize the interaction (690 Hz) between the two nuclear spins. From the measured interaction we derive the spatial configuration of the dimer with atomic-scale resolution. These results indicate that, in combination with advanced material-surface engineering, central spin decoherence under dynamical decoupling control may be a useful probe for nuclear magnetic resonance single-molecule structure analysis.
On-demand semiconductor single-photon source with near-unity indistinguishability
Y. –M. He, Y. He, Y. –J. Wei, D. Wu, M. Atatüre, C. Schneider, *S. Höfling, M. Kamp, *C. –Y. Lu and J. –W. Pan
Nature Nanotechnology 8, 213-217，MARCH 2013
Single-photon sources based on semiconductor quantum dots offer distinct advantages for quantum information, including a scalable solid-state platform, ultrabrightness and interconnectivity with matter qubits. A key prerequisite for their use in optical quantum computing and solid-state networks is a high level of efficiency and indistinguishability. Pulsed resonance fluorescence has been anticipated as the optimum condition for the deterministic generation of high-quality photons with vanishing effects of dephasing. Here, we generate pulsed single photons on demand from a single, microcavity-embedded quantum dot under s-shell excitation with 3 ps laser pulses. The p pulse-excited resonance-fluorescence photons have less than 0.3% background contribution and a vanishing two-photon emission probability. Non-postselective Hong–Ou–Mandel interference between two successively emitted photons is observed with a visibility of 0.97(2), comparable to trapped atoms and ions. Two single photons are further used to implement a high-fidelity quantum ontrolled-NOT gate.
•Topological Superfluids with Finite Momentum Pairing and Majorana Fermions
ChunleiQu, Zhen Zheng, Ming Gong, Yong Xu, Li Mao, XuboZou, GuangcanGuo, Chuanwei Zhang
Nature Communications 4, Article number: 2710 (2013)
•Topological Fulde-Ferrel-Larkin-Ovchinnikov states in Spin-orbit Coupled Fermi Gases
Wei Zhang, and Wei Yi
Nature Communications 4, Article number: 2711(2013)
•Unconventional Superfluid in a Two-Dimensional Fermi gas with Anisotropic Spin-Orbit Coupling and Zeeman fields
Fan Wu, Guang-Can Guo, Wei Zhang, and Wei Yi
Phys. Rev. Lett. 110, 110401 (2013)
Majorana fermions, quantum particles that are their own anti-particles, are not only of fundamental importance in elementary particle physics and dark matter, but also building blocks for fault-tolerant quantum computation. Recently Majorana fermions have been intensively studied in solid state and cold atomic systems. These studies are generally based on superconducting pairing with zero total momentum. On the other hand, finite total momentum Cooper pairings, known as Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) states, were widely studied in many branches of physics. However, whether FFLO superconductors can support Majorana fermions has not been explored. Here we show that Majorana fermions can exist in certain types of gapped FFLO states, yielding a new quantum matter: topological FFLO superfluids/superconductors. We demonstrate the existence of such topological FFLO superfluids and the associated Majorana fermions using spin-orbit coupled degenerate Fermi gases and derive their parameter regions. The implementation of topological FFLO superconductors in semi-conductor/superconductor heterostructures are also discussed.
Pairing in an attractively interacting two-component Fermi gas in the absence of the inversion symmetry and/or the time-reversal symmetry may give rise to exotic superfluid states. Notable examples range from the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state with a finite center-of-mass momentum in a polarized Fermi gas, to the topological superfluid state in a two-dimensional Fermi gas under Rashba spin-orbit coupling and an out-of-plane Zeeman field. Here, we show that a topological FFLO state can be stabilized in a two-dimensional Fermi gas with Rashba spin-orbit coupling and both in-plane and out-of-plane Zeeman fields. We characterize the topological FFLO state by a non-trivial Berry phase, and demonstrate the stability region of the state on the zero-temperature phase diagram. Given its unique properties in both the quasi-particle dispersion spectra and the momentum distribution, signatures of the topological FFLO state can be detected using existing experimental techniques.
We study the phase diagram of a two-dimensional ultracold Fermi gas with the synthetic spin-orbit coupling (SOC) that has recently been realized at the National Institute of Standards and Technology (NIST). Because of the coexistence of anisotropic SOC and effective Zeeman fields in the NIST scheme, the system shows a rich structure of phase separation involving exotic gapless superfluid states and Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) pairing states with different center-of-mass momenta. In particular, we characterize the stability region of FFLO states and demonstrate their unique features under SOC. We then show that the effective transverse Zeeman field in the NIST scheme can qualitatively change the landscape of the thermodynamic potential which leads to intriguing effects such as the disappearance of pairing instability, the competition between different FFLO states, and the stabilization of a fully gapped FFLO state. These interesting features may be probed, for example, by measuring the in situ density profiles or by the momentum-resolved radio-frequency spectroscopy.
Nuclear Magnetic Resonance Spectroscopy on a (5-Nanometer)(3) Sample Volume
T. Staudacher, F. Shi, S. Pezzagna, J. Meijer, J. Du, C. A. Meriles, F. Reinhard, and J. Wrachtrup
SCIENCE 339, 6119, 561-563, FEB 1 2013
Application of nuclear magnetic resonance (NMR) spectroscopy to nanoscale samples has remained an elusive goal, achieved only with great experimental effort at subkelvin temperatures. We demonstrated detection of NMR signals from a (5-nanometer)(3) voxel of various fluid and solid organic samples under ambient conditions. We used an atomic-size magnetic field sensor, a single nitrogen-vacancy defect center, embedded similar to 7 nanometers under the surface of a bulk diamond to record NMR spectra of various samples placed on the diamond surface. Its detection volume consisted of only 10(4) nuclear spins with a net magnetization of only 10(2) statistically polarized spins.
Ultrafast universal quantum control of a quantum-dot charge qubit using Landau–Zener–Stückelberg interference
Gang Cao,Hai-OuLi,TaoTu,LiWang,ChengZhou,MingXiao,Guang-Can Guo,Hong-Wen Jiang &Guo-Ping Guo
Nature Communications4, Article number: 1401(2013)
A basic requirement for quantum information processing is the ability to universally control the state of a single qubit on timescales much shorter than the coherence time. Although ultrafast optical control of a single spin has been achieved in quantum dots, scaling up such methods remains a challenge. Here we demonstrate complete control of the quantum-dot charge qubit on the picosecond scale. We observe tunable qubit dynamics in a charge-stability diagram, in a time domain, and in a pulse amplitude space of the driven pulse. The observations are well described by Landau–Zener–Stückelberg interference. These results establish the feasibility of a full set of all-electrical single-qubit operations. Although our experiment is carried out in a solid-state architecture, the technique is independent of the physical encoding of the quantum information and has the potential for wider applications.
Noise-resilient quantum evolution steered by dynamical decoupling
Gang-Qin Liu, Hoi Chun Po, Jiangfeng Du, Ren-Bao Liu, and Xin-Yu Pan
NATURE COMMUNICATIONS 4 , 2254 ,AUG 2013
Realistic quantum computing is subject to noise. Therefore, an important frontier in quantum computing is to implement noise-resilient quantum control over qubits. At the same time, dynamical decoupling can protect the coherence of qubits. Here we demonstrate non-trivial quantum evolution steered by dynamical decoupling control, which simultaneously suppresses noise effects. We design and implement a self-protected controlled-NOT gate on the electron spin of a nitrogen-vacancy centre and a nearby carbon-13 nuclear spin in diamond at room temperature, by employing an engineered dynamical decoupling control on the electron spin. Final state fidelity of 0.91(1) is observed in preparation of a Bell state using the gate. At the same time, the qubit coherence time is elongated at least 30 fold. The design scheme does not require the dynamical decoupling control to commute with the qubit interaction and therefore works for general qubit systems. This work marks a step towards implementing realistic quantum computing systems.
Role of point defects on the reactivity of reconstructed
anatase titanium dioxide (001) surface
Wang,Y (Wang, Yang); Sun, HJ(Sun, Hui-Juan); Tan, SJ(Tan, Shi-jing); Feng, H (Feng, Hao); Cheng, ZW (Cheng, Zheng-Wang); Zhao, J*(Zhao, Jin); Zhao, AD (Zhao, Ai-Di); Wang, B* (Wang, Bing); Luo, Y(Luo, Yi); Yang, JL(Yang, Jin-long); Hou, JG (Hou, Jian-Guo)
Nature Communications4, 3214，JUL 2013
The chemical reactivity of different surfaces of titanium dioxide (TiO2) has been the subject of extensive studies in recent decades. The anatase TiO2(001) and its (1×4) reconstructed surfaces were theoretically considered to be the most reactive and have been heavily pursued by synthetic chemists. However, the lack of direct experimental verification or determination of the active sites on these surfaces has caused controversy and debate. Here we report a systematic study on an anatase TiO2(001)-(1×4) surface by means of microscopic and spectroscopic techniques in combination with first-principles calculations. Two types of intrinsic point defects are identified, among which only the Ti3+ defect site on the reduced surface demonstrates considerable chemical activity. The perfect surface itself can be fully oxidized, but shows no obvious activity. Our findings suggest that the reactivity of the anatase TiO2(001) surface should depend on its reduction status, similar to that of rutile TiO2 surfaces.
2013 Top Ten Scientific Research Nomination
of School of Physical Sciences, USTC
Quantum Key Distribution
Y. Liu, T. –Y. Chen, L. –J. Wang, H. Liang, G.-L. Shentu, J. Wang, K. Cui, H. –L. Yin, N.-L. Liu, L. Li, X. Ma, J. S. Pelc, M. M. Fejer, C. –Z. Peng, Q. Zhang, and J. –W. Pan
Physical Review Letters 111, 130502 ，7 SEPTEMBER 2013
Quantum key distribution is proven to offer unconditional security in communication between two remote users with ideal source and detection. Unfortunately, ideal evices never exist in practice and device imperfections have become the targets of various attacks. By developing up-conversion singlephoton detectors with high efficiency and low noise, we faithfully demonstrate the measurement-deviceindependent quantum-key-distribution protocol, which is immune to all hacking strategies on detection.
Meanwhile, we employ the decoy-state method to defend attacks on a nonideal source. By assuming a trusted source scenario, our practical system, which generates more than a 25 kbit secure key over a 50 km fiber link, serves as a stepping stone in the quest for unconditionally secure communications with realistic devices.
Experimental Recovery of Quantum Correlations in Absence of System-Environment Back-Action
Jin-Shi Xu, Kai Sun, Chuan-Feng Li, Xiao-Ye Xu, Guang-Can Guo, Rosario Lo Franco, Giuseppe Compagno, Erika Andersson
Nature Communications4, Article number: 2851(2013)
Revivals of quantum correlations in composite open quantum systems are a useful dynamical feature against detrimental effects of the environment. Their occurrence is attributed to flows of quantum information back and forth from systems to quantum environments. However, revivals also show up in models where the environment is classical, thus unable to store quantum correlations, and forbids system-environment back-action. This phenomenon opens basic issues about its interpretation involving the role of classical environments, memory effects, collective effects and system-environment correlations. Moreover, an experimental realization of back-action-free quantum revivals has applicative relevance as it leads to recover quantum resources without resorting to more demanding structured environments and correction procedures. Here we introduce a simple two-qubit model suitable to address these issues. We then report an all-optical experiment which simulates the model and permits us to recover and control, against decoherence, quantum correlations without back-action. We finally give an interpretation of the phenomenon by establishing the roles of the involved parties.
Room temperature multiferroicity in Bi(4.2)K(0.8)Fe(2)O(9+δ).
Y. W. Yin, J. D. Burton, Y-M. Kim, A. Y. Borisevich, S. J. Pennycook,
Nature Materials12, 397–402 (2013)
Magnetoelectric multiferroics are materials that have coupled magnetic and electric dipole orders, which can bring novel physical phenomena and offer possibilities for new device functions. In this report, single-crystalline Bi(4.2)K(0.8)Fe(2)O(9+δ) nanobelts which are isostructural with the high-temperature superconductor Bi(2)Sr(2)CaCu(2)O(8+δ) are successfully grown by a hydrothermal method. The regular stacking of the rock salt slabs and the BiFeO(3)-like perovskite blocks along the c axis of the crystal makes the Bi(4.2)K(0.8)Fe(2)O(9+δ) nanobelts have a natural magnetoelectric-dielectric superlattice structure. The most striking result is that the bulk material made of the Bi(4.2)K(0.8)Fe(2)O(9+δ) nanobelts is of multiferroicity near room temperature accompanied with a structure anomaly. When an external magnetic field is applied, the electric polarization is greatly suppressed, and correspondingly, a large negative magnetocapacitance coefficient is observed around 270 K possibly due to the magnetoelectric coupling effect. Our result provides contributions to the development of single phase multiferroics.
Evidence for the spin-0 nature of the Higgs boson using ATLAS data
Phys. Lett. B 726 (2013) 120
Studies of the spin and parity quantum numbers of the Higgs boson are presented, based on proton-proton collision data collected by the ATLAS experiment at the LHC. The Standard Model spin-parity JP = 0+ hypothesis is compared with alternative hypotheses using the Higgs boson decays H->gamma gamma, H -> ZZ -> 4 leptons and H->WW -> l nu l nu, as well as the combination of these channels. The analysed dataset corresponds to an integrated luminosity of 20.7 fb-1 collected at a centre-of-mass energy of sqrt(s) = 8 TeV. For the H -> ZZ -> 4-lepton decay mode the dataset corresponding to an integrated luminosity of 4.6 fb-1 collected at sqrt(s) = 7 TeV is added. The data are compatible with the Standard Model JP = 0+ quantum numbers for the Higgs boson, whereas all alternative hypotheses studied in this letter, namely some specific JP = 0-; 1+; 1-; 2+ models, are excluded at confidence levels above 97.8%. This exclusion holds independently of the assumptions on the coupling strengths to the Standard Model particles and in the case of the JP = 2+ model, of the relative fractions of gluon-fusion and quark-antiquark production of the spin-2 particle. The data thus provide evidence for the spin-0 nature of the Higgs boson, with positive parity being strongly preferred.
Universal properties of the Higgs resonance in (2+1)-dimensional U(1) critical systems
Kun Chen, Longxiang Liu, Youjin Deng, Lode Pollet, Nikolay Prokof'ev
Physical Review Letters 110, 170403， 26 APRIL 2013
We present spectral functions for the magnitude squared of the order parameter in the scaling limit of the two-dimensional superﬂuid to Mott insulator quantum phase transition at constant density, which has emergent particle-hole symmetry and Lorentz invariance. The universal functions for the superﬂuid, Mott insulator, and normal liquid phases reveal a low-frequency resonance which is relatively sharp and is followed by a damped oscillation (in the ﬁrst two phases only) before saturating to the quantum critical plateau. The counterintuitive resonance feature in the insulating and normal phases calls for deeper understanding of collective modes in the strongly coupled (2 þ 1)-dimensional relativistic ﬁeld theory.Our results are derived from analytically continued correlation functions obtained from path-integral Monte Carlo simulations of the Bose-Hubbard model.
Experimental Quantum Computing to Solve Systems of Linear Equations
X. -D. Cai, C. Weedbrook, Z. -E. Su, M. -C. Chen, Mile Gu, M. -J. Zhu, L. Li*, N. –L. Liu*, C. –Y. Lu*, and J. –W. Pan
Physical Review Letters 110, 230501，7 JUNE 2013
Solving linear systems of equations is ubiquitous in all areas of science and engineering. With rapidly growing data sets, such a task can be intractable for classical computers, as the best known classical algorithms require a time proportional to the number of variables N. A recently proposed quantum algorithm shows that quantum computers could solve linear systems in a time scale of order logeNT, giving
an exponential speedup over classical computers. Here we realize the simplest instance of this algorithm, solving 2 _ 2 linear equations for various input vectors on a quantum computer.We use four quantum bits and four controlled logic gates to implement every subroutine required, demonstrating the working principle of this algorithm.
Lower bound on the speed of nonlocal correlations without loopholes
J. Yin, Y. Cao, H. –L. Yong, J. –G. Ren, H. Liang, S. –K. Liao, F. Zhou, C. Liu, Y. –P. Wu, G. –S. Pan, L. Li, N. –L. Liu, Q. Zhang, C. –Z. Peng, and J. –W. Pan
Physical Review Letters110, 260407，28 JUNE 2013
In their well-known paper, Einstein, Podolsky, and Rosen called the nonlocal correlation in quantum entanglement a ‘‘spooky action at a distance.’’ If the spooky action does exist, what is its speed? All previous experiments along this direction have locality and freedom-of-choice loopholes. Here, we strictly closed the loopholes by observing a 12 h continuous violation of the Bell inequality and concluded that the
lower bound speed of spooky action was 4 orders of magnitude of the speed of light if Earth’s speed in any inertial reference frame was less than 10_3 time the speed of light.
Berry curvature and 4-dimensional monopole in relativistic chiral kinetic equation
Jiunn-Wei Chen, Shi Pu, Qun Wang, Xin-Nian Wang
Physical Review Letters110,262301(2013)
The Berry phase is a topological phase factor acquired by an eigen-energy state when it undergoes adiabatic evolution along a loop in parameter space. It is in close analogy to the Aharonov-Bohm phase when a charged particle moves in a loop enclosing a magnetic flux, while the Berry curvature is like the magnetic field. The integral of the Berry curvature over a closed surface can be quantized as integers known as Chern-Simons numbers, which is similar to the Dirac magnetic monopole and has deep connection with the quantum Hall effect. The Berry phase is a beautiful, simple and universal structure in quantum physics and has many interesting applications.
A relativistic chiral kinetic equation with manifest Lorentz covariance from Wigner functions of spin-1/2 massless fermions in a constant background electromagnetic field has recently been obtained by Prof. Qun Wang and Dr. Shi Pu from Department of Modern Physics with their collaborators Prof. Jiunn-wei Chen from National Taiwan University and Prof. Xin-nian Wang from Central China Normal University. It contains vorticity terms and a 4-dimensional Euclidean Berry monopole which gives axial anomaly. By integrating out the zero-th component of the 4-momentum p, we reproduce the previous 3-dimensional results derived from the Hamiltonian approach, together with the newly derived vorticity terms. The phase space continuity equation has an anomalous source term proportional to the product of electric and magnetic fields. This provides a unified interpretation of the chiral magnetic and vortical effects, chiral anomaly, Berry curvature, and the Berry monopole in the framework of Wigner functions. This work is supported by the NSFC under grant No. 11125524.
Phase Estimation with Weak Measurement Using a White Light Source
Xiao-Ye Xu, YaronKedem, Kai Sun, Lev Vaidman, Chuan-Feng Li, and Guang-Can Guo
Phys. Rev. Lett.111, 033604 (2013)
We report results of a high precision phase estimation based on a weak measurement scheme using a commercial light-emitting diode. The method is based on a measurement of the imaginary part of the weak value of a polarization operator. The imaginary part of the weak value appeared due to the measurement interaction itself. The sensitivity of our method is equivalent to resolving light pulses of the order of aattosecond and it is robust against chromatic dispersion.
Indistinguishable Tunable Single Photons Emitted by Spin-Flip Raman Transitions in InGaAs Quantum Dots
Yu He , Yu-Ming He ,Y.-J. Wei, X. Jiang, M.-C. Chen, F.-L. Xiong, Y. Zhao, Christian Schneider,Martin Kamp, Sven Ho¨fling, Chao-Yang Lu, and Jian-Wei Pan
Physical Review Letters 111, 237403， 6 DECEMBER 2013
This Letter reports all-optically tunable and highly indistinguishable single Raman photons from a driven single quantum dot spin. The frequency, linewidth, and lifetime of the Raman photons are tunable by varying the driving field power and detuning. Under continuous-wave excitation, subnatural linewidth single photons from off-resonant Raman scattering show an indistinguishability of 0.98(3). Under _ pulse
excitation, spin- and time-tagged Raman fluorescence photons show an almost vanishing multiphoton emission probability of 0.01(2) and a two-photon quantum interference visibility of 0.95(3). Lastly, Hong- Ou-Mandel interference is demonstrated between two single photons emitted from remote, independent quantum dots with an unprecedented visibility of 0.87(4).
(School of Physical Sciences)
On May 11, the Nature Publishing Group released Nature Publishing Index 2010 China, remarking “a dramatic rise in the quality of research being published by China”. University of Science and Technology of China is ranked 3rd of TOP 10 Institutions in Index 2010 China.
This article came from News Center of USTC.