Quantum Information Research Research Articles

Development of a measurement system enabling the reconstruction of γ-ray time spectra by simultaneous recording of energy and time information

We developed a measurement system that enables the reconstruction of γ-ray time spectra in cascade decay schemes with 0.3 ns time resolution, which is sufficient for nuclear decay with more than nanoseconds half-life. As this system records all the time and energy information of γ-rays, the energy regions for the γ-ray identification can be optimized after the measurement. Moreover, this system has five timing inputs and thus we can record the timing data of external perturbations; we can investigate the responses to the perturbation afterward. This property fulfills the demands required for quantum information research with γ-rays.

Clifford recompilation for faster classical simulation of quantum circuits

Simulating quantum circuits classically is an important area of research in quantum information, with applications in computational complexity and validation of quantum devices. One of the state-of-the-art simulators, that of Bravyi et al, utilizes a randomized sparsification technique to approximate the output state of a quantum circuit by a stabilizer sum with a reduced number of terms. In this paper, we describe an improved Monte Carlo algorithm for performing randomized sparsification. This algorithm reduces the runtime of computing the approximate state by the factorℓ/m, whereℓandmare respectively the total and non-Clifford gate counts. The main technique is a circuit recompilation routine based on manipulating exponentiated Pauli operators. The recompilation routine also facilitates numerical search for Clifford decompositions of products of non-Clifford gates, which can further reduce the runtime in certain cases by reducing the 1-norm of the vector of expansion,‖a‖1. It may additionally lead to a framework for optimizing circuit implementations over a gate-set, reducing the overhead for state-injection in fault-tolerant implementations. We provide a concise exposition of randomized sparsification, and describe how to use it to estimate circuit amplitudes in a way which can be generalized to a broader class of gates and states. This latter method can be used to obtain additive error estimates of circuit probabilities with a faster runtime than the full techniques of Bravyi et al. Such estimates are useful for validating near-term quantum devices provided that the target probability is not exponentially small.

Growth of High-Purity Low-Strain Fluorescent Nanodiamonds

Fluorescent emitters in diamond have far-reaching potential applications in areas like quantum information, advanced biosensing, and materials research (especially magnetic and superconductor mater...

Experimental Quantum Switching for Exponentially Superior Quantum Communication Complexity.

Finding exponential separation between quantum and classical information tasks is like striking gold in quantum information research. Such an advantage is believed to hold for quantum computing but is proven for quantum communication complexity. Recently, a novel quantum resource called the quantum switch-which creates a coherent superposition of the causal order of events, known as quantum causality-has been harnessed theoretically in a new protocol providing provable exponential separation. We experimentally demonstrate such an advantage by realizing a superposition of communication directions for a two-party distributed computation. Our photonic demonstration employs d-dimensional quantum systems, qudits, up to d=2^{13} dimensions and demonstrates a communication complexity advantage, requiring less than (0.696±0.006) times the communication of any causally ordered protocol. These results elucidate the crucial role of the coherence of communication direction in achieving the exponential separation for the one-way processing task, and open a new path for experimentally exploring the fundamentals and applications of advanced features of indefinite causal structures.

Controllable radiation properties of a driven exciton-biexciton quantum dot couples to a graphene sheet

We investigate the radiation properties of a driven exciton-biexciton structure quantum dot placed close to a graphene sheet. The study of the Purcell factor then demonstrates the tunability of light-matter coupling, which in turn provides the possibility to control the steady-state populations. As the result, dipole transitions can be selectively enhanced and asymmetry in the resonance fluorescence can be observed. Meanwhile, both quadratures can exhibit two-mode squeezing at the Rabi sideband frequencies. A further study shows that although the increase in the environment temperature has a destructive influence on the population imbalance, squeezing occurs even at room temperature. Due to the flexibility in controlling the resonance fluorescence spectrum and producing two-mode squeezed states, our proposal would have potential applications in quantum information and other quantum research fields.

Efficient classical simulation of the Deutsch\u2013Jozsa and Simon\u2019s algorithms

A long-standing aim of quantum information research is to understand what gives quantum computers their advantage. This requires separating problems that need genuinely quantum resources from those for which classical resources are enough. Two examples of quantum speed-up are the Deutsch–Jozsa and Simon’s problem, both efficiently solvable on a quantum Turing machine, and both believed to lack efficient classical solutions. Here we present a framework that can simulate both quantum algorithms efficiently, solving the Deutsch–Jozsa problem with probability 1 using only one oracle query, and Simon’s problem using linearly many oracle queries, just as expected of an ideal quantum computer. The presented simulation framework is in turn efficiently simulatable in a classical probabilistic Turing machine. This shows that the Deutsch–Jozsa and Simon’s problem do not require any genuinely quantum resources, and that the quantum algorithms show no speed-up when compared with their corresponding classical simulation. Finally, this gives insight into what properties are needed in the two algorithms and calls for further study of oracle separation between quantum and classical computation.

Charge-tunable indium gallium nitride quantum dots

III-Nitride quantum dots have emerged as a new chip-scale system for quantum information science, which combines electrical and optical interfaces on a semiconductor chip that is compatible with non-cryogenic operating temperatures. Yet most work has been limited to optical excitations. To enable single-spin based quantum optical and quantum information research, we demonstrate here quantized charging in optically active, site-controlled III-Nitride quantum dots. Single-electron charging was confirmed by the voltage dependence of the energy, dipole moment, fine structures and polarization properties of the exciton states in the quantum dots. The fundamental energy structures of the quantum dots were identified, including neutral and charged excitons, fine structures of excitons, and A and B excitons. The results lay the ground for coherent control of single charges in III-Nitride QDs, opening a door to III-Nitride based spintronics and spin-qubit quantum information processing.

Electronic Enhancement of the Exciton Coherence Time in Charged Quantum Dots.

Minimizing decoherence due to coupling of a quantum system to its fluctuating environment is at the forefront of quantum information and photonics research. Nature sets the ultimate limit, however, given by the strength of the system's coupling to the electromagnetic field. Here, we establish the ability to electronically control this coupling and enhance the optical coherence time of the charged exciton transition in quantum dots embedded in a photonic waveguide. By manipulating the electronic wave functions through an applied lateral electric field, we increase the coherence time from ∼1.4 to ∼2.7 ns. Numerical calculations reveal that longer coherence arises from the separation of charge carriers by up to ∼6 nm, which leads to a 30% weaker transition dipole moment. The ability to electronically control the coherence time opens new avenues for quantum communication and novel coupling schemes between distant qubits.

Generation of bright squeezed light at 1.5 m telecommunication band and its Wigner function reconstruction

The squeezed light at 1.5 m telecommunication band has been considered as an important resource of continuous variable (CV) practical fiber-based quantum information research because it is the lowest loss in fiber. A bright phase quadrature squeezed light for continuous variable at 1.5 m is demonstrated from a semi-monolithic degenerate optical parametric amplifier (DOPA) based on a periodically poled KTiOPO4 (PPKTP) crystal. The laser source is a continuous wave (CW) single-frequency fiber laser at 1.5 m, which is sent through a ring mode cleaner (MC) as a preliminary spatial and noise filter. And then the main portion of the output from the MC is used for external-enhanced second harmonic generation to obtain a CW single-frequency low noise laser at 780 nm that acts as the pump of the DOPA. The residual light of the output from the MC at 1.5 m is used as the injected signal light of the DOPA and the local oscillator (LO) of a balanced homodyne detector (BHD) system. The DOPA is built by using a type-I PPKTP crystal and a piezo-actuated output coupler and works in double-resonance case with a threshold power of 230 mW. When the DOPA is operating in the state of amplification, the output down-conversion field should be a bright phase quadrature squeezed light, where the relative phase between the pump and the injected signal is locked to 0. A 4.7 dB bright phase quadrature squeezed light is measured by the BHD system with the pump light of 110 mW and the injected signal of 3 mW, where the relative phase between the down-conversion field and the LO is locked to 0. Our measurement is limited by the optical losses and the detection efficiency. We have taken into account the detection efficiency of 86.6%, and the actual squeezing of the squeezed light being 6.3 dB. Moreover, because it is so crucial a process for CV quantum information system that the transmission and evolution of the CV squeezed states in the fiber may reappear in all information of the quantum states in the phase space, then the bright squeezed light is detected by a BHD system in the time domain, and its Wigner quasi-probability distribution function can be reconstructed by using a quantum tomographic technique. Furthermore, the bright squeezed state at 1.5 m is an ideal source for fiber-based long-distance quantum information because of its stability and bright mean field.

Ball-grid array architecture for microfabricated ion traps

State-of-the-art microfabricated ion traps for quantum information research are approaching nearly one hundred control electrodes. We report here on the development and testing of a new architecture for microfabricated ion traps, built around ball-grid array (BGA) connections, that is suitable for increasingly complex trap designs. In the BGA trap, through-substrate vias bring electrical signals from the back side of the trap die to the surface trap structure on the top side. Gold-ball bump bonds connect the back side of the trap die to an interposer for signal routing from the carrier. Trench capacitors fabricated into the trap die replace area-intensive surface or edge capacitors. Wirebonds in the BGA architecture are moved to the interposer. These last two features allow the trap die to be reduced to only the area required to produce trapping fields. The smaller trap dimensions allow tight focusing of an addressing laser beam for fast single-qubit rotations. Performance of the BGA trap as characterized with 40Ca+ ions is comparable to previous surface-electrode traps in terms of ion heating rate, mode frequency stability, and storage lifetime. We demonstrate two-qubit entanglement operations with 171Yb+ ions in a second BGA trap.

4P 분석을 통한 양자점 기술개발 현황 분석 -양자점 기술의 응용 및 융합 분야를 중심으로

Quantum dot technology can be complementary application of the bulk material, and that a wide range of applications that can take advantage of the characteristic convergence technology. With the development of quantum dot technology, it is important to analyze Marketability of quantum technology, business opportunity. In this study, patents, papers, market, analysis of the project will be to investigate the quantum information research trends. Research results are expected to be used as a basis for research and development path setting and strategic planning of the quantum dot. In particular, this study found the performance of quantum dot research through patents and papers analyzed. In addition, fast-growing field, the field to lead the commercialization were derived. Compared to the advanced research and national research was to diagnose the domestic research into quantum dots.

Informação e teoria quântica

A pesquisa em informação quântica sugere uma íntima conexão entre o conceito de informação e a teoria quântica, mas essa conexão envolve nuances cuja análise é o objeto deste trabalho. A sabedoria comum nesse campo divide-se em duas grandes áreas, não excludentes entre si. Há os que são movidos pela possibilidade de uso da teoria quântica em um novo campo, o da computação, independentemente do esclarecimento de seus fundamentos, aqui incluído o conceito de "informação". Alguns consideram que estamos diante de um grande problema conceitual sem resposta satisfatória no momento, enquanto que outros, dentre os que reconhecem a magnitude do problema, têm proposto formulações com a pretensão de solução do problema. Este artigo tem pretensões modestas. Não pretendemos aportar novas soluções ao problema, nem apoiar uma das soluções existentes. Temos a expectativa de através da análise histórico-conceitual do problema mapear as diversas possibilidades, apontando o que nos parecem ser aspectos fortes e fracos nessas possibilidades.

Quantum communication with an accelerated partner

An unsolved problem in relativistic quantum information research is how to model efficient, directional quantum communication between localised parties in a fully quantum field theoretical framework. We propose a tractable approach to this problem based on solving the Heisenberg evolution of localized field observables. We illustrate our approach by analysing, and obtaining approximate analytical solutions to, the problem of communicating coherent states between an inertial sender, Alice and an accelerated receiver, Rob. We use these results to determine the efficiency with which continuous variable quantum key distribution could be carried out over such a communication channel.

Quantum Optics and Quantum Information with Twin Photon

In the non-linear process called parametric down-conversion, it is possible to perform frequency conversion in the optical domain. For instance, when one laser beam shines a non-linear crystal, some of its photons are converted into two new photons with frequencies that are different from the frequency of the incident laser. This process is also called parametric down-conversion, because it is based in spontaneous emmission. The pair of photons obtained, are produced basically in the same instant of time, then they are called twin photons. Moreover, besides simultaneity, they also share a non-factorable quantum state. This property makes these photons a very special tool, because they are in an entangled state for some degrees of freedom and they can be prepared in an entangled state for other ones. In this talk, I will discuss the motivation of Quantum Computation and Quantum Communication, present the concept of Quantum Entanglement, and discuss the application of photoic entanglement for the understanding of the Foundations of Quantum Mechanics and the research in Quantum Information.

Spin Path Integrals and Generations

The spin of a free electron is stable but its position is not. Recent quantum information research by G. Svetlichny, J. Tolar, and G. Chadzitaskos have shown that the Feynman \emph{position} path integral can be mathematically defined as a product of incompatible states; that is, as a product of mutually unbiased bases (MUBs). Since the more common use of MUBs is in finite dimensional Hilbert spaces, this raises the question "what happens when \emph{spin} path integrals are computed over products of MUBs?" Such an assumption makes spin no longer stable. We show that the usual spin-1/2 is obtained in the long-time limit in three orthogonal solutions that we associate with the three elementary particle generations. We give applications to the masses of the elementary leptons.

Collisional population transfer in trappedYb+ions

Long-lived metastable states of Yb+ ions are used for atomic frequency standards, precision measurements, and quantum information research. The effect of population trapping and transfer in these states must be well understood. We report here the transfer of Yb+ ions into the long-lived {sup 2}F{sub 7/2} state by means of collisions between He buffer gas and Yb+ ions held in a linear Paul trap. Transfer rates were measured as functions of buffer-gas pressure and repump-laser power, and the collisional population transfer rates were extracted. The measured transfer rate coefficients are 8.32(75)x10-11 and 8.65(33)x10-11 cm3/s for the collisional processes {sup 2}P{sub 1/2}{yields}{sup 2}D{sub 5/2} and {sup 2}D{sub 3/2}{yields}{sup 2}F{sub 7/2}, respectively.

Solid state atomic processors for light

This paper is devoted to optics in rare earth ion doped crystal at low temperature. In cryogenic conditions, interesting features come from absorption rather than from transparency. The optical transition linewidth is considerably reduced, which also corresponds to a strong increase of quantum state lifetime. Linewidth narrowing leads to signal processing applications. Specific use for RADAR warning receivers is considered here. Then the quantum lifetime extension is illustrated by coherent transient processes that represent necessary experimental steps on the way to quantum information research.

Rare Earth Doped Crystals for Quantum Information: Quantum Computing and Quantum Storage

Quantum information uses special properties of quantum systems to manipulate or transmit data. This results in new processes, which are impossible to obtain with classical devices. For example, quantum computing and quantum storage, which are two important fields in quantum information research, aim respectively at performing very fast calculations and at storing quantum states of photons. These two applications could be obtained in solid-state systems using rare earth doped crystals. In this context, the most important property of these materials is the long coherence lifetimes of rare earth ion optical and hyperfine transitions. This allows one to create long-lived superposition states, which is a fundamental requirement for efficient quantum computing and storage. Promising results have already been demonstrated in rare earth doped crystals but it will be difficult to improve them with current materials. In this paper, we discuss the general and specific requirements for rare earth ions and crystals in order to perform quantum computing with a large number of quantum bits as well as all solid-state quantum storage. We also present the properties of a few recently studied crystals: Ho3+:YVO4, Ho3+:LuVO4 (quantum computing) and Tm3+:Y3Al5O12 (quantum storage).

Quantum entanglement in carbon nanotubes.

With the surge of research in quantum information, the issue of producing entangled states has gained prominence. Here, we show that judiciously bringing together two systems of strongly interacting electrons with vastly differing ground states-the gapped BCS superconductor and the Luttinger liquid-can result in quantum entanglement. We propose three sets of measurements involving single-walled metallic carbon nanotubes which have been shown to exhibit Luttinger liquid physics, to test our claim and as nanoscience experiments of interest in and of themselves.