Implementation Of Quantum Logic Research Articles

Estimate of the time required to perform a nonadiabatic holonomic quantum computation

Nonadiabatic holonomic quantum computation has been proposed as a method to implement quantum logic gates with robustness comparable to that of adiabatic holonomic gates but with shorter execution times. In this paper, we establish an isoholonomic inequality for quantum gates, which provides a lower bound on the lengths of cyclic transformations of the computational space that generate a specific gate. Then, as a corollary, we derive a nonadiabatic execution time estimate for holonomic gates. In addition, we demonstrate that under certain dimensional conditions, the isoholonomic inequality is tight in the sense that every gate on the computational space can be implemented holonomically and unitarily in a time-optimal way. We illustrate the results by showing that the procedures for implementing a universal set of holonomic gates proposed in a pioneering paper on nonadiabatic holonomic quantum computation saturate the isoholonomic inequality and are thus time optimal. Published by the American Physical Society 2024

From digital to quantum epidemiology: The Quantum Data Lake concept for big data related to viral infectious diseases

The development of quantum epidemiology represents the next anticipated phase in epidemiology transformation, driven by the emergence of new quantum technologies. Epidemiology is currently transitioning into the digital era and undergoing a paradigm shift from a data-driven to a value-driven strategy. Epidemiology data are characterized by uncertainty, multidimensionality, and disconnection, thereby correlating with the preferential quantum approach for data exposition, value creation, and modeling. Examples of such complex epidemiology data include the data on DNA viruses with associated symptoms and diseases. The Quantum Data Lake concept is proposed and consists of several layers and quantum tools, including Robson semantic triples, Quantum Universal Exchange Language, Hyperbolic Dirac Net, “quantum ribosome” structure, quantum random access memory, teleportation, Quantum Query Language, non-Hermitian gates, and tensor networks (e.g., matrix product state, projected entangled pair state, and multiscale entanglement renormalization ansatz [MERA]), alongside PT-symmetry properties. PT-symmetry can serve as an intuitive modeling tool, and PT-symmetry breaking can detect the hidden shift in the information that is permanently updated in the Data Lake. The computational output is presented as PT-symmetry gain/loss equilibrium breaking in the form of a complex number, i.e., two possible variants of epidemic modeling. For MERA, non-Hermiticity with spontaneous PT-symmetry breaking can theoretically appear as a violation of the entanglement monotonicity and local entanglement gain, leading to a non-reversible character of the coarse-graining transformation. The duality of PT-symmetry equilibrium breaking can be compared to, for example, the estimation of the best and worst scenarios simultaneously, or the gain of entanglement can display a significant correlation between some studied parameters embedded into the data. The fundamental difference between digital and quantum epidemiology is the implementation of quantum logic and reliance on a quantum theory.

Characterization and Coherent Control of Spin Qubits with Modulated Electron Beam and Resonator

AbstractThe coherent dynamics and control of spin qubits are fundamental requirements for the development and implementation of quantum technology. However, controlling a single spin qubit within a set of qubits is challenging due to the spatial extent of the applied magnetic field, which can negatively impact the coherent dynamics of neighboring qubits. In this study, a scheme is proposed for characterizing and controlling the coherent dynamics of spin qubits. The proposed scheme comprises a resonator that encloses the desired quantum system and a modulated electron beam that passes through the resonator in close proximity to the qubit of interest. The scheme involves solving the quantum master equation with Lindblad terms to obtain the system's dynamics. Reliability of the proposed model is validated by testing it on a potassium atom, 41K, and an NV‐ center in diamond. The results demonstrate that by controlling the parameters of the resonator and electron beam, the coherence and decoherence rates of these quantum systems can be enhanced. The proposed scheme has the potential to characterize various types of spin‐based quantum systems and implement quantum logic gates for quantum computation .

Dynamics of one two-level-atom interacting with a multiple cavity modes

We discuss how to implement quantum logic gates by considering a two-level-atom driven by a strong microwave field and successively interacting with m+1 cavity modes. The scheme is insensitive to the initial state of the atom, and the operation time is independent of the number of cavity modes involved in the system operations. This scheme is used to realize two quantum logic gates (m-target-qubit controlled-global-phase gate and Multi-qubit phase shift gate) in a time much shorter than the photonic lifetime. We also studied the influence of decoherence on the fidelity. In general, our system is reasonably less sensitive to the photonic and atomic decay rates and therefore it can be experimentally realized.

Quantum Fredkin and Toffoli gates on a versatile programmable silicon photonic chip

Quantum logic gates are backbones of quantum information processing (QIP), wherein the typical three-qubit Fredkin and Toffoli gates are essential in quantum computation and communication. So far, the quantum Fredkin gate has only been demonstrated with pre-entangled input states in free-space optics, which limits its usage for independent input photons. Here, we put forward an exquisite scheme and experimentally perform a proof-of-principle demonstration of three-qubit Fredkin and Toffoli gates on a programmable quantum photonic chip. Our scheme can also be used to realize a series of other two-qubit quantum gates. Our work sheds light on the merits of quantum photonic chip in implementing quantum logic gates, and paves the way for advanced quantum chip processors.

Minimization of the micromotion of trapped ions with artificial neural networks

Minimizing the micromotion of a trapped ion in a linear Paul trap is of great importance in maintaining long coherence time as well as implementing quantum logic gates with high fidelity, which is crucial for large-scale quantum computation with trapped ions. Here, by applying the RF (radio frequency)-photon correlation technique, we demonstrate that a machine learning method based on artificial neural networks can quickly search for optimal voltage settings of the electrodes to minimize the trapped ion's micromotion. This machine learning assisted RF-photon correlation technique can be straightforwardly applied to more complicated surface ion traps with many electrodes, where the manual minimization of the excess micromotion generated by stray electric fields would become extremely challenging for the larger number of electrodes with various voltage settings. Instead, the presented machine learning assisted method provides an effective and automatic way to address this need.

Heralded quantum gates for hybrid systems via waveguide-mediated photon scattering

Universal quantum gates play a critical role in quantum information processing. Here, based on the scattering property of photons off single emitters in one-dimensional waveguides, we present some heralded protocols for realizing controlled-not, Toffoli, and Fredkin gates on hybrid systems. The control qubit of our gates is encoded on a flying photon, and the target qubits are encoded in the degenerate ground states of the emitter. In our schemes, the faulty scattering processes between emitters and photons caused by system imperfections can be transformed into the detection of photon polarization. That is, our three quantum gates are accomplished in a heralded way. Moreover, the quantum circuits for the three gates are versatile and compact, and no additional qubits are required. With current technique on manipulating the emitter-waveguide system, our protocols may be experimentally feasible. This work provides an effective avenue for implementing quantum logic gates.

Quantum Logic Spectroscopy with Ions in Thermal Motion.

A mixed-species geometric phase gate has been proposed for implementing quantum logic spectroscopy on trapped ions, which combines probe and information transfer from the spectroscopy to the logic ion in a single pulse. We experimentally realize this method, show how it can be applied as a technique for identifying transitions in currently intractable atoms or molecules, demonstrate its reduced temperature sensitivity, and observe quantum-enhanced frequency sensitivity when it is applied to multi-ion chains. Potential applications include improved readout of trapped-ion clocks and simplified error syndrome measurements for quantum error correction.

Photon Enhanced Interaction and Entanglement in Semiconductor Position-Based Qubits

CMOS technologies facilitate the possibility of implementing quantum logic in silicon. In this work, we discuss a minimalistic modelling of entangled photon communication in semiconductor qubits. We demonstrate that electrostatic actuation is sufficient to construct and control desired potential energy profiles along a Si quantum dot (QD) structure allowing the formation of position-based qubits. We further discuss a basic mathematical formalism to define the position-based qubits and their evolution under the presence of external driving fields. Then, based on Jaynes–Cummings–Hubbard formalism, we expand the model to include the description of the position-based qubits involving four energy states coupled with a cavity. We proceed with showing an anti-correlation between the various quantum states. Moreover, we simulate an example of a quantum trajectory as a result of transitions between the quantum states and we plot the emitted/absorbed photos in the system with time. Lastly, we examine the system of two coupled position-based qubits via a waveguide. We demonstrate a mechanism to achieve a dynamic interchange of information between these qubits over larger distances, exploiting both an electrostatic actuation/control of qubits and their photon communication. We define the entanglement entropy between two qubits and we find that their quantum states are in principle entangled.

Quantum logic using correlated one-dimensional quantum walks

Quantum Walks are unitary processes describing the evolution of an initially localized wavefunction on a lattice potential. The complexity of the dynamics increases significantly when several indistinguishable quantum walkers propagate on the same lattice simultaneously, as these develop non-trivial spatial correlations that depend on the particle’s quantum statistics, mutual interactions, initial positions, and the lattice potential. We show that even in the simplest case of a quantum walk on a one dimensional graph, these correlations can be shaped to yield a complete set of compact quantum logic operations. We provide detailed recipes for implementing quantum logic on one-dimensional quantum walks in two general cases. For non-interacting bosons—such as photons in waveguide lattices—we find high-fidelity probabilistic quantum gates that could be integrated into linear optics quantum computation schemes. For interacting quantum-walkers on a one-dimensional lattice—a situation that has recently been demonstrated using ultra-cold atoms—we find deterministic logic operations that are universal for quantum information processing. The suggested implementation requires minimal resources and a level of control that is within reach using recently demonstrated techniques. Further work is required to address error-correction.

Multi-crossing dynamics of a multi-particle Landau-Zener (LZ) system: Dynamics matrix approach

This paper investigates multi-crossing dynamics of multi-particle Landau-Zener (LZ) systems applying Dynamic matrix approach (DMA) that is found to generalize probability amplitudes. It is also observed that for exceedingly low frequencies, the system exhibits one crossing while for high frequencies, the multi-crossing. It is shown that for particular phenomenological parameters of the system, there is total population transfer that achieves the values one or zero useful for implementing quantum logic gates.

Beating Classical Computing Without a Quantum Computer

Photons performing quantum random walks can be used to calculate matrix properties without actually implementing quantum logic gates. [Also see Reports by Childs et al. , Broome et al. , and Spring et al. ]

Implementing quantum logic gates with gradient ascent pulse engineering: principles and practicalities

We briefly describe the use of gradient ascent pulse engineering (GRAPE) pulses to implement quantum logic gates in nuclear magnetic resonance quantum computers, and discuss a range of simple extensions to the core technique. We then consider a range of difficulties that can arise in practical implementations of GRAPE sequences, reflecting non-idealities in the experimental systems used.

Spin tunneling in the diamond color center coupled to theP1center

The spin-1 carried by the nitrogen-vacancy (NV${}^{\ensuremath{-}}$) color center of a diamond is a promising candidate as a quantum bit (qubit) for the realization of a solid-state quantum computer. The interaction with the $P1$ center, which is a single substitutional nitrogen atom with spin-$\frac{1}{2}$, converts the NV${}^{\ensuremath{-}}$ qubit to a multilevel system. The 18-level energy diagram of the NV${}^{\ensuremath{-}}$-$P1$ coupled defect pair exhibits several level anticrossings and the spin functions change sign at different values of the applied magnetic field. Beyond each resonance, the two electronic spins of the coupled triplet-doublet system flip individually or in concert, offering possibilities to implement quantum logic gates. Interlevel transitions are also possible. The transition probabilities can be predicted rigorously in the framework of the Landau-Zener theory. The spin flip occurs by quantum tunneling. It is also possible to introduce geometric phases, which can be useful for the realization of phase gates.

Controlling quantum information processing in hybrid systems on chips

We investigate quantum information processing, transfer and storage in hybrid systems comprised of diverse blocks integrated on chips. Strong coupling between superconducting (SC) qubits and ensembles of ultracold atoms or NV-center spins is mediated by a microwave transmission-line resonator that interacts near-resonantly with the atoms or spins. Such hybrid devices allow us to benefit from the advantages of each block and compensate for their disadvantages. Specifically, the SC qubits can rapidly implement quantum logic gates, but are noisy (prone to decoherence), while collective states of the atomic or spin ensemble are quiet(protected from decoherence) and thus can be employed for storage of quantum information. To improve the overall performance (fidelity) of such devices we discuss dynamical control to optimize quantum state-transfer from a noisy qubit to the quiet storage ensemble. We propose to maximize the fidelity of transfer and storage in a spectrally inhomogeneous spin ensemble, by pre-selecting the optimal spectral portion of the ensemble. Significant improvements of the overall fidelity of hybrid devices are expected under realistic conditions. Experimental progress towards the realization of these schemes is discussed.

Observation of the Stark-Tuned Förster Resonance between Two Rydberg Atoms

Cold atoms in highly excited Rydberg states are promising candidates to implement quantum logic gates of a quantum computer via long-range dipole-dipole interaction. Two-qubit gates require a controlled interaction of only two close Rydberg atoms. We report on the first spectroscopic observation of the resonant dipole-dipole interaction between two cold rubidium Rydberg atoms confined in a small laser excitation volume. The interaction strength was controlled by fine-tuning of the Rydberg levels into a Förster resonance using the Stark effect. The observed resonance line shapes are in good agreement with numerical Monte Carlo simulations.

All-optical switching using the quantum Zeno effect and two-photon absorption

We have previously shown that the quantum Zeno effect can be used to implement quantum logic gates for quantum computing applications, where the Zeno effect was produced using a strong two-photon absorbing medium. Here we show that the Zeno effect can also be used to implement classical logic gates whose inputs and outputs are high-intensity fields (coherent states). The operation of the devices can be understood using a quasistatic analysis, and their switching times are calculated using a dynamic approach. The two-photon absorption coefficient of rubidium vapor is shown to allow operation of these devices at relatively low power levels.

Scheme for implementing quantum logic gates for two atoms trapped in different cavities

A scheme is presented for realizing quantum logic gates for two atoms localized in two distant optical cavities. Our scheme works in a regime in which the atom–cavity coupling strength is smaller than the cavity decay rate. Thus the requirement on the quality factor of the cavities is greatly relaxed. Furthermore, the fidelity of our scheme is not affected by detection inefficiency and atomic decay. These advantages are important in view of experiment.

Quantum interference of tunnel trajectories between states of different spin length in a dimeric molecular nanomagnet

An experimental study of a ‘dimeric’ single-molecule magnet—consisting of two coupled half-wheels of spin 7/2 each—provides evidence for quantum interference between the two sub-systems. Tunable electron spins in solid media are among the most promising candidates for qubits1. In this context, molecular nanomagnets have been proposed as hardware for quantum computation2. The flexibility in their synthesis represents a distinct advantage over other spin systems, enabling the systematic production of samples with desirable properties, for example, with a view to implementing quantum logic gates3,4. Here, we report the observation of quantum interference associated with tunnelling trajectories between states of different total spin length in a dimeric molecular nanomagnet. We argue that the interference is a consequence of the unique characteristics of a molecular Mn12 wheel, which behaves as a molecular dimer with weak ferromagnetic exchange coupling: each half of the molecule acts as a single-molecule magnet, whereas the weak coupling between the two halves gives rise to an extra internal spin degree of freedom within the molecule—that is, its total spin may fluctuate. More importantly, the observation of quantum interference provides clear evidence for quantum-mechanical superpositions involving entangled states shared between both halves of the wheel.

One Electron Makes Current Flow

Even the smallest components in a modern desktop computer use tens of thousands of electrons at a time to implement classical logic (the conventional 1s and 0s of binary computation). A computer that operated on single electrons, however, could in principle implement quantum logic functions (quantum bits or “qubits” that could perform computational tasks that are beyond the ability of classical computers). One proposed architecture for a single-electron computer could be realized in a two-dimensional electron gas (2DEG), a special kind of reservoir in which electrons can travel without dissipation (1). On page 1169 of this issue, Fève et al. (2) report on an important step toward this vision: a device that can emit single electrons into a 2DEG and absorb them again on nanosecond time scales. With such a controllable electron source, researchers will now be able to set up one or more electrons in well-defined quantum states, which are crucial for any future quantum computer.