Showing papers on "Qubit published in 2011"
TL;DR: Superconducting circuits based on Josephson junctions exhibit macroscopic quantum coherence and can behave like artificial atoms as mentioned in this paper, and it is possible to implement atomic-physics and quantum-optics experiments on a chip using these artificial atoms.
Abstract: Superconducting circuits based on Josephson junctions exhibit macroscopic quantum coherence and can behave like artificial atoms. Recent technological advances have made it possible to implement atomic-physics and quantum-optics experiments on a chip using these artificial atoms. This Review presents a brief overview of the progress achieved so far in this rapidly advancing field. We not only discuss phenomena analogous to those in atomic physics and quantum optics with natural atoms, but also highlight those not occurring in natural atoms. In addition, we summarize several prospective directions in this emerging interdisciplinary field.
1,132 citations
TL;DR: In this article, a colloquium-style introduction to the midgap excitations in superconductors known as Majorana fermions is given, along with strategies to detect them in a topological superconductor, as well as possible applications in a quantum computer.
Abstract: This is a colloquium-style introduction to the midgap excitations in superconductors known as Majorana fermions. These elusive particles, equal to their own antiparticle, may or may not exist in Nature as elementary building blocks, but in condensed matter they can be constructed out of electron and hole excitations. What is needed is a superconductor to hide the charge difference, and a topological (Berry) phase to eliminate the energy difference from zero-point motion. A pair of widely separated Majorana fermions, bound to magnetic or electrostatic defects, has non-Abelian exchange statistics. A qubit encoded in this Majorana pair is expected to have an unusually long coherence time. We discuss strategies to detect Majorana fermions in a topological superconductor, as well as possible applications in a quantum computer. The status of the experimental search is reviewed.
Contents:
I. What Are They? (Their origin in particle physics; Their emergence in superconductors; Their potential for quantum computing)
II. How to Make Them (Shockley mechanism; Chiral p-wave superconductors; Topological insulators; Semiconductor heterostructures)
III. How to Detect Them (Half-integer conductance quantization; Nonlocal tunneling; 4\pi-periodic Josephson effect; Thermal metal-insulator transition)
IV. How to Use Them (Topological qubits; Read out; Braiding)
V. Outlook on the Experimental Progress
[scheduled for vol. 4 of Annual Review of Condensed Matter Physics]
1,008 citations
TL;DR: In this paper, the authors reported the creation of Greenberger-Horne-Zeilinger states with up to 14 qubits by investigating the coherence of up to 8 ions over time and observed a decay proportional to the square of the number of qubits.
Abstract: We report the creation of Greenberger-Horne-Zeilinger states with up to 14 qubits. By investigating the coherence of up to 8 ions over time, we observe a decay proportional to the square of the number of qubits. The observed decay agrees with a theoretical model which assumes a system affected by correlated, Gaussian phase noise. This model holds for the majority of current experimental systems developed towards quantum computation and quantum metrology.
1,008 citations
TL;DR: In this article, a superconducting qubit was used to probe the noise spectrum of a spin system with an energy-relaxation time T 1 = 12 μs.
Abstract: Quantum coherence in natural and artificial spin systems is fundamental to applications ranging from quantum information science to magnetic-resonance imaging and identification. Several multipulse control sequences targeting generalized noise models have been developed to extend coherence by dynamically decoupling a spin system from its noisy environment. In any particular implementation, however, the efficacy of these methods is sensitive to the specific frequency distribution of the noise, suggesting that these same pulse sequences could also be used to probe the noise spectrum directly. Here we demonstrate noise spectroscopy by means of dynamical decoupling using a superconducting qubit with energy-relaxation time T1 =12 μs. We first demonstrate that dynamical decoupling improves the coherence time T 2 in this system up to the T2 =2 T1 limit (pure dephasing times exceeding 100 μs), and then leverage its filtering properties to probe the environmental noise over a frequency (f) range 0.2-20 MHz, observing a 1/fα distribution with α < 1. The characterization of environmental noise has broad utility for spin-resonance applications, enabling the design of optimized coherent-control methods, promoting device and materials engineering, and generally improving coherence. © 2011 Macmillan Publishers Limited. All rights reserved.
698 citations
TL;DR: The preparation and measurement of a multi-spin quantum register in a low-temperature solid-state system is demonstrated by implementing resonant optical excitation techniques originally developed in atomic physics, and compatibility with qubit control is shown.
Abstract: Initialization and read-out of coupled quantum systems are essential ingredients for the implementation of quantum algorithms. Single-shot read-out of the state of a multi-quantum-bit (multi-qubit) register would allow direct investigation of quantum correlations (entanglement), and would give access to further key resources such as quantum error correction and deterministic quantum teleportation. Although spins in solids are attractive candidates for scalable quantum information processing, their single-shot detection has been achieved only for isolated qubits. Here we demonstrate the preparation and measurement of a multi-spin quantum register in a low-temperature solid-state system by implementing resonant optical excitation techniques originally developed in atomic physics. We achieve high-fidelity read-out of the electronic spin associated with a single nitrogen-vacancy centre in diamond, and use this read-out to project up to three nearby nuclear spin qubits onto a well-defined state. Conversely, we can distinguish the state of the nuclear spins in a single shot by mapping it onto, and subsequently measuring, the electronic spin. Finally, we show compatibility with qubit control: we demonstrate initialization, coherent manipulation and single-shot read-out in a single experiment on a two-qubit register, using techniques suitable for extension to larger registers. These results pave the way for a test of Bell's inequalities on solid-state spins and the implementation of measurement-based quantum information protocols.
690 citations
TL;DR: It is demonstrated that several defect spin states in the 4H polytype of SiC (4H-SiC) can be optically addressed and coherently controlled in the time domain at temperatures ranging from 20 to 300 kelvin.
Abstract: Electronic spins in semiconductors have been used extensively to explore the limits of external control over quantum mechanical phenomena. A long-standing goal of this research has been to identify or develop robust quantum systems that can be easily manipulated, for future use in advanced information and communication technologies. Recently, a point defect in diamond known as the nitrogen-vacancy centre has attracted a great deal of interest because it possesses an atomic-scale electronic spin state that can be used as an individually addressable, solid-state quantum bit (qubit), even at room temperature. These exceptional quantum properties have motivated efforts to identify similar defects in other semiconductors, as they may offer an expanded range of functionality not available to the diamond nitrogen-vacancy centre. Notably, several defects in silicon carbide (SiC) have been suggested as good candidates for exploration, owing to a combination of computational predictions and magnetic resonance data. Here we demonstrate that several defect spin states in the 4H polytype of SiC (4H-SiC) can be optically addressed and coherently controlled in the time domain at temperatures ranging from 20 to 300 kelvin. Using optical and microwave techniques similar to those used with diamond nitrogen-vacancy qubits, we study the spin-1 ground state of each of four inequivalent forms of the neutral carbon-silicon divacancy, as well as a pair of defect spin states of unidentified origin. These defects are optically active near telecommunication wavelengths, and are found in a host material for which there already exist industrial-scale crystal growth and advanced microfabrication techniques. In addition, they possess desirable spin coherence properties that are comparable to those of the diamond nitrogen-vacancy centre. This makes them promising candidates for various photonic, spintronic and quantum information applications that merge quantum degrees of freedom with classical electronic and optical technologies.
669 citations
TL;DR: The digital approach to quantum simulation in a system of trapped ions is demonstrated and evidence that the level of control required for a full-scale device is within reach is provided.
Abstract: A digital quantum simulator is an envisioned quantum device that can be programmed to efficiently simulate any other local system. We demonstrate and investigate the digital approach to quantum simulation in a system of trapped ions. With sequences of up to 100 gates and 6 qubits, the full time dynamics of a range of spin systems are digitally simulated. Interactions beyond those naturally present in our simulator are accurately reproduced, and quantitative bounds are provided for the overall simulation quality. Our results demonstrate the key principles of digital quantum simulation and provide evidence that the level of control required for a full-scale device is within reach.
614 citations
TL;DR: In this article, a study of GaAs quantum dots was conducted to provide a fuller understanding of the memory loss and how it can be suppressed, and two orders of magnitude longer than previously reported for this system.
Abstract: Electron spins in semiconductor structures are quantum bits with good prospects, but the information stored in the spin states tends to degrade quickly owing to interactions with nuclei in the host material. A study of GaAs quantum dots now provides a fuller understanding of this memory loss and how it can be suppressed. Quantum-memory times exceeding 200 μs are demonstrated, two orders of magnitude longer than previously reported for this system.
505 citations
Journal Article•
TL;DR: The coherence times achieved here are sufficient for the conversion of an electronic qubit into a photon, which can serve as a flying qubit for long-distance quantum communication.
440 citations
TL;DR: An all-microwave two-qubit gate on superconducting qubits which are fixed in frequency at optimal bias points and tunable via the amplitude of microwave irradiation on one qubit at the transition frequency of the other is demonstrated.
Abstract: We demonstrate an all-microwave two-qubit gate on superconducting qubits which are fixed in frequency at optimal bias points. The gate requires no additional subcircuitry and is tunable via the amplitude of microwave irradiation on one qubit at the transition frequency of the other. We use the gate to generate entangled states with a maximal extracted concurrence of 0.88, and quantum process tomography reveals a gate fidelity of 81%.
412 citations
TL;DR: In this article, a waveguide single-photon detector based on superconducting nanowires on GaAs ridge waveguides is proposed to provide high efficiency (20%) at telecom wavelengths, high timing accuracy (60 ps), response time in the ns range, and is fully compatible with the integration of singlephoton sources, passive networks and modulators.
Abstract: The generation, manipulation and detection of quantum bits (qubits) encoded on single photons is at the heart of quantum communication and optical quantum information processing. The combination of single-photon sources, passive optical circuits and single-photon detectors enables quantum repeaters and qubit amplifiers, and also forms the basis of all-optical quantum gates and of linear-optics quantum computing. However, the monolithic integration of sources, waveguides and detectors on the same chip, as needed for scaling to meaningful number of qubits, is very challenging, and previous work on quantum photonic circuits has used external sources and detectors. Here we propose an approach to a fully-integrated quantum photonic circuit on a semiconductor chip, and demonstrate a key component of such circuit, a waveguide single-photon detector. Our detectors, based on superconducting nanowires on GaAs ridge waveguides, provide high efficiency (20%) at telecom wavelengths, high timing accuracy (60 ps), response time in the ns range, and are fully compatible with the integration of single-photon sources, passive networks and modulators.
TL;DR: Using a hybrid quantum circuit combining a superconducting qubit and an ensemble of electronic spins, a superposition of the qubit states is prepared that is stored into collective excitations of the spin ensemble and retrieved back into the qubits later on.
Abstract: We report the experimental realization of a hybrid quantum circuit combining a superconducting qubit and an ensemble of electronic spins. The qubit, of the transmon type, is coherently coupled to the spin ensemble consisting of nitrogen-vacancy centers in a diamond crystal via a frequency-tunable superconducting resonator acting as a quantum bus. Using this circuit, we prepare a superposition of the qubit states that we store into collective excitations of the spin ensemble and retrieve back into the qubit later on. These results constitute a proof of concept of spin-ensemble based quantum memory for superconducting qubits.
TL;DR: This work continuously measure the state of a superconducting quantum bit coupled to a microwave readout cavity by using a fast, ultralow-noise parametric amplifier to enable quantum error correction and feedback--essential components of quantum information processing.
Abstract: We continuously measure the state of a superconducting quantum bit coupled to a microwave readout cavity by using a fast, ultralow-noise parametric amplifier. This arrangement allows us to observe quantum jumps between the qubit states in real time, and should enable quantum error correction and feedback--essential components of quantum information processing.
TL;DR: This work embedded an artificial atom, a superconducting transmon qubit, in an open transmission line and investigated the strong scattering of incident microwave photons, using two-tone spectroscopy to study scattering from excited states and electromagnetically induced transparency (EIT).
Abstract: We have embedded an artificial atom, a superconducting transmon qubit, in an open transmission line and investigated the strong scattering of incident microwave photons (similar to 6 GHz). When an input coherent state, with an average photon number N << 1 is on resonance with the artificial atom, we observe extinction of up to 99.6% in the forward propagating field. We use two-tone spectroscopy to study scattering from excited states and we observe electromagnetically induced transparency (EIT). We then use EIT to make a single-photon router, where we can control to what output port an incoming signal is delivered. The maximum on-off ratio is around 99% with a rise and fall time on the order of nanoseconds, consistent with theoretical expectations. The router can easily be extended to have multiple output ports and it can be viewed as a rudimentary quantum node, an important step towards building quantum information networks.
TL;DR: The approach, which involves integrating the quantum control mechanism into the trapping device in a scalable manner, could be applied to quantum information processing, simulation and spectroscopy.
Abstract: Control over physical systems at the quantum level is important in fields as diverse as metrology, information processing, simulation and chemistry. For trapped atomic ions, the quantized motional and internal degrees of freedom can be coherently manipulated with laser light. Similar control is difficult to achieve with radio-frequency or microwave radiation: the essential coupling between internal degrees of freedom and motion requires significant field changes over the extent of the atoms' motion, but such changes are negligible at these frequencies for freely propagating fields. An exception is in the near field of microwave currents in structures smaller than the free-space wavelength, where stronger gradients can be generated. Here we first manipulate coherently (on timescales of 20 nanoseconds) the internal quantum states of ions held in a microfabricated trap. The controlling magnetic fields are generated by microwave currents in electrodes that are integrated into the trap structure. We also generate entanglement between the internal degrees of freedom of two atoms with a gate operation suitable for general quantum computation; the entangled state has a fidelity of 0.76(3), where the uncertainty denotes standard error of the mean. Our approach, which involves integrating the quantum control mechanism into the trapping device in a scalable manner, could be applied to quantum information processing, simulation and spectroscopy.
TL;DR: In this paper, it was shown that the spin state of an electron localized to the nitrogen-vacancy centre can be transferred to the nuclear spin, where it can be stored until needed.
Abstract: A nitrogen impurity in diamond—where two of the carbon atoms are replaced by a nitrogen atom and a vacant lattice site—is seen as a valuable qubit. The spin of an electron localized to the nitrogen-vacancy centre is commonly used for processing. Researchers now show that this electron spin state can be transferred to the nitrogen nuclear spin, where it can be stored until needed.
TL;DR: In this article, the authors implemented multiple quantum error correction cycles for phase-flip errors on qubits encoded with trapped ions using high-fidelity gate operations and a reset technique for the auxiliary qubits.
Abstract: The computational potential of a quantum processor can only be unleashed if errors during a quantum computation can be controlled and corrected for. Quantum error correction works if imperfections of quantum gate operations and measurements are below a certain threshold and corrections can be applied repeatedly. We implement multiple quantum error correction cycles for phase-flip errors on qubits encoded with trapped ions. Errors are corrected by a quantum-feedback algorithm using high-fidelity gate operations and a reset technique for the auxiliary qubits. Up to three consecutive correction cycles are realized, and the behavior of the algorithm for different noise environments is analyzed.
TL;DR: The most fundamental implementation of such a quantum memory is demonstrated, by mapping arbitrary polarization states of light into and out of a single atom trapped inside an optical cavity, which makes the system a versatile quantum node with excellent prospects for applications in optical quantum gates and quantum repeaters.
Abstract: Efficient, high-fidelity storage and exchange of quantum information between light and an optical quantum memory is essential for long-distance quantum communication, quantum networking and distributed quantum computing. Stephan Ritter and colleagues demonstrate the most fundamental implementation of such a quantum memory, mapping arbitrary polarization states of light into and out of single atoms trapped inside an optical cavity. The high fidelity (93%) and relatively long qubit coherence time of this atomic memory make it a versatile quantum node, with excellent prospects for applications in optical quantum gates and quantum repeaters. The faithful storage of a quantum bit (qubit) of light is essential for long-distance quantum communication, quantum networking and distributed quantum computing1. The required optical quantum memory must be able to receive and recreate the photonic qubit; additionally, it must store an unknown quantum state of light better than any classical device. So far, these two requirements have been met only by ensembles of material particles that store the information in collective excitations2,3,4,5,6,7. Recent developments, however, have paved the way for an approach in which the information exchange occurs between single quanta of light and matter8,9,10,11,12,13. This single-particle approach allows the material qubit to be addressed, which has fundamental advantages for realistic implementations. First, it enables a heralding mechanism that signals the successful storage of a photon by means of state detection14,15,16; this can be used to combat inevitable losses and finite efficiencies. Second, it allows for individual qubit manipulations, opening up avenues for in situ processing of the stored quantum information. Here we demonstrate the most fundamental implementation of such a quantum memory, by mapping arbitrary polarization states of light into and out of a single atom trapped inside an optical cavity. The memory performance is tested with weak coherent pulses and analysed using full quantum process tomography. The average fidelity is measured to be 93%, and low decoherence rates result in qubit coherence times exceeding 180 microseconds. This makes our system a versatile quantum node with excellent prospects for applications in optical quantum gates17 and quantum repeaters18.
TL;DR: Evidence of coherent strong coupling between a single macroscopic superconducting artificial atom (a flux qubit) and an ensemble of electron spins in the form of nitrogen–vacancy colour centres in diamond provides a foundation for future quantum memories and hybrid devices coupling microwave and optical systems.
Abstract: During the past decade, research into superconducting quantum bits (qubits) based on Josephson junctions has made rapid progress. Many foundational experiments have been performed, and superconducting qubits are now considered one of the most promising systems for quantum information processing. However, the experimentally reported coherence times are likely to be insufficient for future large-scale quantum computation. A natural solution to this problem is a dedicated engineered quantum memory based on atomic and molecular systems. The question of whether coherent quantum coupling is possible between such natural systems and a single macroscopic artificial atom has attracted considerable attention since the first demonstration of macroscopic quantum coherence in Josephson junction circuits. Here we report evidence of coherent strong coupling between a single macroscopic superconducting artificial atom (a flux qubit) and an ensemble of electron spins in the form of nitrogen-vacancy colour centres in diamond. Furthermore, we have observed coherent exchange of a single quantum of energy between a flux qubit and a macroscopic ensemble consisting of about 3 × 10(7) such colour centres. This provides a foundation for future quantum memories and hybrid devices coupling microwave and optical systems.
TL;DR: In this paper, a general optomechanical system for converting photons to phonons in an efficient and reversible manner is described, based on coupled photonic and phononic crystal planar circuits.
Abstract: In this paper, we describe a general optomechanical system for converting photons to phonons in an efficient and reversible manner. We analyze classically and quantum mechanically the conversion process and proceed to a more concrete description of a phonon–photon translator (PPT) formed from coupled photonic and phononic crystal planar circuits. The application of the PPT to RF-microwave photonics and circuit QED, including proposals utilizing this system for optical wavelength conversion, long-lived quantum memory and state transfer from optical to superconducting qubits, is considered.
TL;DR: In this paper, the authors present a reliable algorithm to evaluate quantum discord for general two-qubit states, amending and extending an approach recently put forward for the subclass of $X$ states.
Abstract: We present a reliable algorithm to evaluate quantum discord for general two-qubit states, amending and extending an approach recently put forward for the subclass of $X$ states. A closed expression for the discord of arbitrary states of two qubits cannot be obtained, as the optimization problem for the conditional entropy requires the solution to a pair of transcendental equations in the state parameters. We apply our algorithm to run a numerical comparison between quantum discord and an alternative, computable measure of nonclassical correlations, namely, the geometric discord. We identify the extremally nonclassically correlated two-qubit states according to the (normalized) geometric discord, at a fixed value of the conventional quantum discord. The latter cannot exceed the square root of the former for systems of two qubits.
TL;DR: The first integrated photonic controlled-NOT (CNOT) gate for polarization-encoded qubits is demonstrated, demonstrating its high fidelity to the expected one and the ability of this gate to transform separable states into entangled ones and vice versa.
Abstract: As quantum information processing continues to develop apace, the need for integrated photonic devices becomes ever greater for both fundamental measurements and technological applications. To this end, Crespi et al. demonstrate a high-fidelity photonic controlled-NOT gate on a glass chip.
TL;DR: In this paper, the authors derived a master equation that takes into account the qubit-resonator coupling and showed that the failure of the quantum optical master equation is manifest in the ultrastrong coupling regime.
Abstract: Cavity and circuit QED study light-matter interaction at its most fundamental level. Yet, this interaction is most often neglected when considering the coupling of this system with an environment. In this paper, we show how this simplification, which leads to the standard quantum optics master equation, is at the root of unphysical effects. Including qubit relaxation and dephasing, and cavity relaxation, we derive a master equation that takes into account the qubit-resonator coupling. Special attention is given to the ultrastrong coupling regime, where the failure of the quantum optical master equation is manifest. In this situation, our model predicts an asymmetry in the vacuum Rabi splitting that could be used to probe dephasing noise at unexplored frequencies. We also show how fluctuations in the qubit frequency can cause sideband transitions, squeezing, and Casimir-like photon generation.
TL;DR: In this article, the authors proposed the use of quantum mechanical phenomena that pose limitations on the continued shrinking of conventional information processing devices, such as silicon, to build a quantum computer.
Abstract: Quantum computers hold the promise of massive performance enhancements across a range of applications, from cryptography and databases to revolutionary scientific simulation tools. Such computers would make use of the same quantum mechanical phenomena that pose limitations on the continued shrinking of conventional information processing devices. Many of the key requirements for quantum computing differ markedly from those of conventional computers. However, silicon, which plays a central part in conventional information processing, has many properties that make it a superb platform around which to build a quantum computer.
TL;DR: In this paper, a simple algorithm to evaluate the quantum discord for two-qubit $X$ states was proposed by Ali, Rau, and Alber with minimization taken over only a few cases.
Abstract: Quantum discord provides a measure for quantifying quantum correlations beyond entanglement and is very hard to compute even for two-qubit states because of the minimization over all possible measurements. Recently a simple algorithm to evaluate the quantum discord for two-qubit $X$ states was proposed by Ali, Rau, and Alber [Phys. Rev. A 81, 042105 (2010)] with minimization taken over only a few cases. Here we shall at first identify a class of $X$ states, whose quantum discord can be evaluated analytically without any minimization, for which their algorithm is valid, and also identify a family of $X$ states for which their algorithm fails. And then we demonstrate that this special family of $X$ states provides furthermore an explicit example for the inequivalence between the minimization over positive operator-valued measures and that over von Neumann measurements.
TL;DR: Here it is shown how a single electron may be captured in a surface acoustic wave minimum and transferred from one quantum dot to a second, unoccupied, dot along a long, empty channel.
Abstract: Electrons strongly interact with other electrons and their environment, making it extremely difficult to isolate and detect a single moving electron in a similar way to single photons in quantum optics experiments. But now, in two unrelated reports, Hermelin et al. and McNeil et al. demonstrate that it is possible to emit a single electron from one quantum dot and detect it again with high efficiency after longevity propagation over several micrometres to another quantum dot. The single electron is isolated from other electrons as it is sent into a one-dimensional channel, where it is carried along on a surface acoustic wave induced by microwave excitation. McNeil et al. also show that the same electron can be transferred back and forth up to 60 times, a total distance of 0.25 millimetres. This work demonstrates a new way of transporting a single quantum particle over a long distance in nanostructures, and could pave the way for a range of quantum optics experiments and for quantum information circuits based on single electrons. Single-electron circuits of the future, consisting of a network of quantum dots, will require a mechanism to transport electrons from one functional part of the circuit to another. For example, in a quantum computer1 decoherence and circuit complexity can be reduced by separating quantum bit (qubit) manipulation from measurement and by providing a means of transporting electrons between the corresponding parts of the circuit2. Highly controlled tunnelling between neighbouring dots has been demonstrated3,4, and our ability to manipulate electrons in single- and double-dot systems is improving rapidly5,6,7,8. For distances greater than a few hundred nanometres, neither free propagation nor tunnelling is viable while maintaining confinement of single electrons. Here we show how a single electron may be captured in a surface acoustic wave minimum and transferred from one quantum dot to a second, unoccupied, dot along a long, empty channel. The transfer direction may be reversed and the same electron moved back and forth more than sixty times—a cumulative distance of 0.25 mm—without error. Such on-chip transfer extends communication between quantum dots to a range that may allow the integration of discrete quantum information processing components and devices.
TL;DR: This work differs from previous efforts in that the cavity-qubit excitations retain a photonic nature rather than a hybridization of qubit and photon and provides the needed tolerance to disorder for future condensed matter experiments.
Abstract: Mediated photon-photon interactions are realized in a superconducting coplanar waveguide cavity coupled to a superconducting charge qubit. These nonresonant interactions blockade the transmission of photons through the cavity. This so-called dispersive photon blockade is characterized by measuring the total transmitted power while varying the energy spectrum of the photons incident on the cavity. A staircase with four distinct steps is observed and can be understood in an analogy with electron transport and the Coulomb blockade in quantum dots. This work differs from previous efforts in that the cavity-qubit excitations retain a photonic nature rather than a hybridization of qubit and photon and provides the needed tolerance to disorder for future condensed matter experiments.
01 May 2011
TL;DR: This work reports the realization of an integrated beam splitter able to support polarization-encoded qubits and demonstrates quantum interference with polarization-entangled states and singlet state projection.
Abstract: We report the realization of an integrated beam splitter able to support polarization-encoded qubits. Using this device, we demonstrate quantum interference with polarization-entangled states and singlet state projection.
TL;DR: Applying sequences of inversion pulses to the qubit system, a method for dynamical decoupling noise spectroscopy is developed that generates effective filter functions that probe the environmental spectral density without requiring assumptions about its shape.
Abstract: Decoherence is one of the most important obstacles that must be overcome in quantum information processing. It depends on the qubit-environment coupling strength, but also on the spectral composition of the noise generated by the environment. If the spectral density is known, fighting the effect of decoherence can be made more effective. Applying sequences of inversion pulses to the qubit system, we developed a method for dynamical decoupling noise spectroscopy. We generate effective filter functions that probe the environmental spectral density without requiring assumptions about its shape. Comparing different pulse sequences, we recover the complete spectral density function and distinguish different contributions to the overall decoherence.
TL;DR: In this article, the polarization of a single optical photon and a solid-state spin qubit associated with thenitrogen vacancy centre in diamond were shown to be entanglement.
Abstract: Quantum entanglement is among the most fascinating aspects of quantum theory. Here we realize quantum entanglement between the polarization of a single optical photon and a solid-state spin qubit associated with thenitrogen vacancy centre in diamond.