Phase Gate Operation Research Articles

Cubic Phase Gate Operation to Decrease the Error of Two-Mode Transformations

Cubic Phase Gate Operation to Decrease the Error of Two-Mode Transformations

Two-way ↔ quantum communication using four-qubit cluster state: Mutual exchange of quantum information

In this study, we have proposed a scheme for two-way quantum communication in which the two legitimate participants mutually exchange their quantum information to each other by using a four-qubit cluster state as the quantum channel. Recently, by utilizing four-qubit cluster state as the quantum channel, Kazemikhah et al. [Int. J. Theor. Phys. 60, 378 (2021)] tried to design a scheme for mutual exchange of quantum information between two legitimate participants. However, in this study, it has been shown that in their scheme, the transmission of quantum information cannot be realized because the two participants are not entangled to each other due to a trivial conceptual mistake made by Kazemikhah et al. in the description of the quantum channel. Here, we have shown that two legitimate participants can teleport quantum information states to each other by using four-qubit cluster state as the quantum channel, provided they co-operate with each other and perform nonlocal controlled phase gate operation. If both participants do not co-operate with each other, then no one can reconstruct the information sent to them, and therefore, the exchange of information is possible only when both participants are honest to each other.

Bidirectional quantum-controlled teleportation using six-qubit cluster state without remote joint operation

Utilizing a six-qubit cluster state as quantum channel, a bidirectional controlled quantum teleportation (BCQT) scheme was put forward by Yan in [Int. J. Theor. Phys. 52, 3870 (2013)]. However, in order to accomplish the task, two agents must cooperate to perform a quantum controlled phase gate operation on their two qubits. In view of the present technique, such kind of remote joint operation is difficult to be realized. In this paper, based on the same cluster state, we propose a different BCQT scheme to avoid the remote joint operation. Besides, an unnecessary waste of classical messages in Yan’s scheme is point out.

Error-transparent operations on a logical qubit protected by quantum error correction

Universal quantum computation is striking for its unprecedented capability in processing information, but its scalability is challenging in practice because of the inevitable environment noise. Although quantum error correction (QEC) techniques have been developed to protect stored quantum information from leading orders of errors, the noise-resilient processing of the QEC-protected quantum information is highly demanded but remains elusive. Here, we demonstrate phase gate operations on a logical qubit encoded in a bosonic oscillator in an error-transparent (ET) manner. Inspired by Refs. [9,10], the ET gates are extended to the bosonic code and are able to tolerate errors during the gate operations, regardless of the random occurrence time of the error. With precisely designed gate Hamiltonians through photon-number-resolved AC-Stark shifts, the ET condition is fulfilled experimentally. We verify that the ET gates outperform the non-ET gates with a substantial improvement of the gate fidelity after an occurrence of the single-photon-loss error. Our ET gates in the superconducting quantum circuits are readily for extending to multiple encoded qubits and a universal gate set is within reach, paving the way towards fault-tolerant quantum computation.

Ultrafast coherent excitation of a 40Ca+ ion

Fast entangling quantum gates can significantly enhance the performance of a trapped-ion quantum computer. In pursuit of implementing a fast two-qubit gate, we investigate the coherent excitation of a 40Ca+ ion with a train of picosecond pulses resonant to the 4S1/2 4P3/2 transition. The optical pulse train is derived from a mode-locked, stabilized optical frequency comb. We implement two techniques to characterize the pulse-ion interaction and show how all requirements can be met for an implementation of a fast phase gate operation.

Deterministically swapping frequency-bin entanglement from photon-photon to atom-photon hybrid systems

Inspired by the recent developments of the research on the atom-photon quantum interface and energy-time entanglement between single-photon pulses, we are motivated to study the deterministic protocol for the frequency-bin entanglement of the atom-photon hybrid system, which is analogous to the frequency-bin entanglement between single-photon pulses. We show that such entanglement arises naturally in considering the interaction between a frequency-bin entangled single-photon pulse pair and a single atom coupled to an optical cavity, via straightforward atom-photon phase gate operations. Its anticipated properties and preliminary examples of its potential application in quantum networking are also demonstrated. Moreover, we construct a specific quantum entanglement witness tool to detect such extended frequency-bin entanglement from a reasonably general set of separable states, and prove its capability theoretically. We focus on the energy-time considerations throughout the analysis.

Spin Ensembles Coupled to Superconducting Resonators: A Scalable Architecture for Solid-State Quantum Computing

A design is proposed for scalable solid-state quantum computing, which is based on collectively enhanced magnetic coupling between nitrogen-vacancy center ensembles and superconducting transmission line resonators interconnected by current-biased Josephson junction superconducting phase qubit. In this hybrid system, we realize distant multi-qubit controlled phase gate operations and generate distant multi-qubit entangled W-like states, being indispensable resource to quantum computation. Our proposed architecture consists of solid-state spin ensembles and circuit QED, and could achieve quantum computing in a solid-state environment with high-fidelity and scalable way. The experimental feasibility is discussed, and the implementation efficiency is demonstrated numerically.

基于操作腔外原子比特控制腔内原子比特相干性时间演化

Considering two atom bits in Bell state initially,one bit was injected into a vacuum cavity to produce resonance while leaving the other outside.The controllable coherence of an atom bit inside the cavity was investigated by manipulating the atom bit outside the cavity.For the cases of before and after the Hadamard,Hadamard-like,Y,and phase logic gate manipulations on the atom bit outside the cavity,the correlation of two kinds of initial Bell state was discussed by numerical calculation.The time evolution curves of off-diagonal elements in the reduced density matrix for the atom bit inside the cavity was studied.The results show that the off-diagonal elements of the density matrix for the atom bit inside the cavity are zero at any moment before operating the atom bit outside the cavity.That is,the atom bit inside the cavity is always in a mixed state or classical states,and its coherence is always suppressed.However,after Hadamard gate and Hadamard-like gate operations and ground state measurements,offdiagonal elements in the reduced density matrix of the atom bit inside the cavity show the 2π period time evolution,and the coherence can be restored except(2n+1)π/2.At nπthe maximal coherence superposition state and general coherence superposition state were prepared,and a R(π/2)rotation correlation existed between the two kinds of Bell states.In addition,performing Y gate and phase gate operations on the outside atom bit,the coherence for the inside atom bit cannot restore.The necessary condition for the restoration of the coherence of the inside atom bit was found out as following:while logic gate operations manipulate the interactions between the atom bit inside the cavity and its environment,and the two atom bits are separated from the field,a strongly coherent entanglement is necessary between the two atom bits.

Quantum phase flip gate based on plasmonic double-bar resonators

We demonstrate a quantum phase flip gate between two QDs that resonantly couple to plasmonic double-bar resonators with asymmetric coupling strengths. Large coupling strengths can be achieved due to the deep subwavelength mode volumes of the optical modes in plasmonic double-bar resonators. High fidelity (~98%) and high success probability of the phase gate operation have been obtained when the coupling strength ratio (g2/g1) and resonant mode decay rate (κ/g1) are optimized. The subwavelength-scale plasmonic structures provide tremendous potential for solid-state quantum information processing.

Quantum Three-Qubit Phase Gate Operation by Using an Artificial Atom in a Three-Mode Cavity

We propose a scheme for realizing quantum three-qubit phase gate operation, in a three-mode cavity where the large detuned cavity-mode fields interact with the four-level artificial atom of an rf-SQUID in tripod-type configuration. In this scheme, the two lowest levels of the artificial atom represent the two logical states of the target qubit and two cavity-mode states are the control qubits, while the third cavity-mode field serves the gate manipulation. Since only the metastable lower levels are involved in the gate operations, the gate is insensitive to the decay rates of the artificial atom, which makes this scheme advantageous and it is important in view of decoherence.

A Scheme for Atomic Entangled States and Quantum Gate Operations in Cavity QED

We propose a scheme for controllably entangling the ground states of five-state W-type atoms confined in a cavity and realizing swap gate and phase gate operations. In this scheme the cavity is only virtually excited and the atomic excited states are almost not occupied, so the produced entangled states and quantum logic operations are very robust against the cavity decay and atomic spontaneous emission.

Repeat-until-success measurement-based scheme for controlled phase gates in a cavity

We propose a new repeat-until-success (RUS) measurement-based scheme to implement quantum controlled phase gates according to the effect of dipole-induced-transparency (DIT) in a cavity and single-photon interference at a 50:50 beam-splitter. In our scheme, the DIT effect can appropriately attach a photon to the state of the dipoles according to their initial state, and in this way, a suitably encoded dipole-photon state is thus prepared. The measurement of the photon after it passing through a 50:50 beam-splitter can project the encoded matter-photon state to either a desired phase gate operation for the matter qubits or to their initial states. The recurrence of the initial state permits us to implement the desired entangling gate in a RUS way.

Coupled quantum electrodynamics in photonic crystal cavities towards controlled phase gate operations

In this paper, a scalable photonic crystal cavity array, in which single embedded quantum dots (QDs) are coherently interacting, is studied theoretically. Firstly, we examine the spectral character and optical delay brought about by the coupled cavities interacting with single QDs, in an optical analogue to electromagnetically induced transparency. Secondly, we then examine the usability of this coupled QD–cavity system for quantum phase gate operation and our numerical examples suggest that a two-qubit system with fidelity above 0.99 and photon loss below 0.04 is possible.

Implementing a conditionalN-qubit phase gate in a largely detuned optical cavity

We propose a scheme to implement an $N$-qubit conditional phase gate with $N$ neutral atoms which are trapped in a large detuning optical cavity. In our scheme, since the cavity field is only required to be virtually excited, the phase gate operation is insensitive to the cavity decay and the gate can be implemented with a high fidelity.

Cavity-QED-based unconventional geometric phase gates with bichromatic field modes

Realization of two-qubit quantum phase gate is demonstrated using unconventional geometric phase in a cavity sustaining bichromatic field modes which are highly detuned from the atomic transition frequency. The two cavity modes are displaced simultaneously and thus acquire a geometric phase which can be used for realization of approximate phase gate operation.

Quantum phase gate for photonic qubits using only beam splitters and postselection

We show that a beam splitter of reflectivity one-third can be used to realize a quantum phase gate operation if only the outputs conserving the number of photons on each side are post-selected.