arXiv subjects

Qi-Ping Su

Publications and source records attributed to Qi-Ping Su.

48 records · Page 3Linked to original sources

arXiv2014

Generating multipartite entangled states of qubits distributed in different cavities

Cavity-based large-scale quantum information processing (QIP) needs a large number of qubits and placing all of them in a single cavity quickly runs into many fundamental and practical problems such as the increase of cavity decay rate and decrease of qubit-cavity coupling strength. Therefore, future QIP most likely will require quantum networks consisting of a large number of cavities, each hosting and coupled to multiple qubits. In this work, we propose a way to prepare a $W$-class entangled state of spatially-separated multiple qubits in different cavities, which are connected to a coupler qubit. Because no cavity photon is excited, decoherence caused by the cavity decay is greatly suppressed during the entanglement preparation. This proposal needs only one coupler qubit and one operational step, and does not require using a classical pulse, so that the engineering complexity is much reduced and the operation is greatly simplified. As an example of the experimental implementation, we further give a numerical analysis, which shows that high-fidelity generation of the $W$ state using three superconducting phase qubits each embedded in a one-dimensional transmission line resonator is feasible within the present circuit QED technique. The proposal is quite general and can be applied to accomplish the same task with other types of qubits such as superconducting flux qubits, charge qubits, quantum dots, nitrogen-vacancy centers and atoms.

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arXiv2014

Single-step transfer or exchange of multipartite quantum entanglement with minimum resources

The transfer or exchange of multipartite quantum states is critical to the realization of large-scale quantum information processing and quantum communication. A challenging question in this context is: What is the minimum resource required and how to simultaneously transfer or exchange multipartite quantum entanglement between two sets of qubits. Finding the answer to these questions is of great importance to quantum information science. In this work, we demonstrate that by using a single quantum two-level system - the simplest quantum object - as a coupler arbitrary multipartite quantum states (either entangled or separable) can be transferred or exchanged simultaneously between two sets of qubits. Our findings offer the potential to significantly reduce the resources needed to construct and operate large-scale quantum information networks consisting of many multi-qubit registers, memory cells, and processing units.

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arXiv2014

Single-step implementation of a multiple-target-qubit controlled phase gate without need of classical pulses

We propose a simple method for realizing a multiqubit phase gate of one qubit simultaneously controlling $n$ target qubits, by using three-level quantum systems (i.e., qutrits) coupled to a cavity or resonator. The gate can be implemented using one operational step and without need of classical pulses, and no photon is populated during the operation. Thus, the gate operation is greatly simplified and decoherence from the cavity decay is much reduced, when compared with the previous proposals. In addition, the operation time is independent of the number of qubits and no adjustment of the qutrit level spacings or the cavity frequency is needed during the operation.

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arXiv2014

Fast and simple scheme for generating NOON states of photons in circuit QED

The generation, manipulation and fundamental understanding of entanglement lies at very heart of quantum mechanics. Among various types of entangled states, the NOON states are a kind of special quantum entangled states with two orthogonal component states in maximal superposition, which have a wide range of potential applications in quantum communication and quantum information processing. Here, we propose a fast and simple scheme for generating NOON states of photons in two superconducting resonators by using a single superconducting transmon qutrit. Because only one superconducting qutrit and two resonators are used, the experimental setup for this scheme is much simplified when compared with the previous proposals requiring a setup of two superconducting qutrits and three cavities. In addition, this scheme is easier and faster to implement than the previous proposals, which require using a complex microwave pulse, or a small pulse Rabi frequency in order to avoid nonresonant transitions.

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arXiv2013

Entanglement generation and quantum information transfer between spatially-separated qubits in different cavities

The generation and control of quantum states of spatially-separated qubits distributed in different cavities constitute fundamental tasks in cavity quantum electrodynamics. An interesting question in this context is how to prepare entanglement and realize quantum information transfer between qubits located at different cavities, which are important in large-scale quantum information processing. In this paper, we consider a physical system consisting of two cavities and three qubits. Two of the qubits are placed in two different cavities while the remaining one acts as a coupler, which is used to connect the two cavities. We propose an approach for generating quantum entanglement and implementing quantum information transfer between the two spatially-separated intercavity qubits. The quantum operations involved in this proposal are performed by a virtual photon process, and thus the cavity decay is greatly suppressed during the operations. In addition, to complete the present tasks, only one coupler qubit and one operation step are needed. Moreover, there is no need of applying classical pulses, so that the engineering complexity is much reduced and the operation procedure is greatly simplified. Finally, our numerical results illustrate that high-fidelity implementation of this proposal using superconducting phase qubits and one-dimenstion transmision line resonators is feasible for current circuit QED implementations. This proposal can also be applied to other types of superconducting qubits, including flux and charge qubits.

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arXiv2013

Preparing Greenberger-Horne-Zeilinger Entangled Photon Fock States of Three Cavities Coupled by a Superconducting Flux Qutrit

We propose a way to prepare Greenberger-Horne-Zeilinger (GHZ) entangled photon Fock states of three cavities, by using a superconducting flux qutrit coupled to the cavities. This proposal does not require the use of classical microwave pulses and measurement during the entire operation. Thus, the operation is greatly simplified and the circuit engineering complexity and cost is much reduced. The proposal is quite general and can be applied to generate three-cavity GHZ entangled photon Fock states when the three cavities are coupled by a different three-level physical system such as a superconducting charge qutrit, a transmon qutrit, or a quantum dot.

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arXiv2013

Generating entanglement between microwave photons and qubits in multiple cavities coupled by a superconducting qutrit

We discuss how to generate entangled coherent states of four \textrm{microwave} resonators \textrm{(a.k.a. cavities)} coupled by a superconducting qubit. We also show \textrm{that} a GHZ state of four superconducting qubits embedded in four different resonators \textrm{can be created with this scheme}. In principle, \textrm{the proposed method} can be extended to create an entangled coherent state of $n$ resonators and to prepare a Greenberger-Horne-Zeilinger (GHZ) state of $n$ qubits distributed over $n$ cavities in a quantum network. In addition, it is noted that four resonators coupled by a coupler qubit may be used as a basic circuit block to build a two-dimensional quantum network, which is useful for scalable quantum information processing.

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arXiv2013

Proposal for implementing the three-qubit refined Deutsch-Jozsa quantum algorithm

We propose a way to implement a three-qubit refined Deutsh-Jozsa (DJ) algorithm. The present proposal is based on the construction of the 35 $f$-controlled phase gates, which uses single-qubit $σ_z$ gates and two-qubit {\it standard} controlled-phase (CP) gates only. This proposal is implementable because a single-qubit $σ_z$ gate can be easily realized by applying a single classical pulse and a two-qubit CP gate has been experimentally demonstrated in various physical systems. Finally, it is noted that this proposal is quite general, and can be applied to implement a three-qubit refined DJ algorithm in a cavity-based or noncavity-based physical system.

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arXiv2013

Simultaneous quantum state exchange or transfer between two sets of cavities and generation of multiple Einstein-Podolsky-Rosen pairs via a superconducting coupler qubit

We propose an approach to simultaneously perform quantum state exchange or transfer between two sets of cavities, each containing $N$ cavities, by using only one superconducting coupler qubit. The quantum states to be exchanged or transferred can be arbitrary pure or mixed states and entangled or nonentangled. The operation time does not increase with the number of cavities, and there is no need of applying classic pulses during the entire operation. Moreover, the approach can be also applied to realize quantum state exchange or transfer between two sets of qubits, such as that between two multi-qubit quantum registers. We further show that the present proposal can be used to simultaneously generate multiple Einstein-Podolsky-Rosen pairs of photons or qubits, which are important in quantum communication. The method can be generalized to other systems by using different types of physical qubit as a coupler to accomplish the same task.

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arXiv2012

Realizing an $n$-target-qubit controlled phase gate in cavity QED: An approach without classical pulses

We propose a way to realize a multiqubit controlled phase gate with one qubit simultaneously controlling $n$ target qubits using atoms in cavity QED. In this proposal, there is no need of using classical pulses during the entire gate operation. The gate operation time scales as $\sqrt{n}$ only and thus the gate can be performed faster when compared with sending atoms through the cavity one at a time. In addition, only three steps of operations are required for realizing this $n$-target-qubit controlled phase gate. This proposal is quite general, which can be applied to other physical systems such as various superconducting qubits coupled to a resonator, NV centers coupled to a microsphere cavity or quantum dots in cavity QED.

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arXiv2012

Proposal for realizing a multiqubit tunable phase gate of one qubit simultaneously controlling n target qubits using cavity QED

We propose a way to realize a multiqubit tunable phase gate of one qubit simultaneously controlling n target qubits with atoms in cavity QED. In this proposal, classical pulses interact with atoms outside a cavity only, thus the experimental challenge of applying a pulse to an intra-cavity single atom without affecting other atoms in the same cavity is avoided. Because of employing a first-order large detuning, the gate can be performed fast when compared with the use of a second-order large detuning. Furthermore, the gate operation time is independent of the number of qubits. This proposal is quite general, which can be applied to various superconducting qubits coupled to a resonator, NV centers coupled to a microsphere cavity or quantum dots in cavity QED.

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arXiv2012

Generation of GHZ entangled states of photons in multiple cavities via a superconducting qutrit or an atom through resonant interaction

We propose an efficient method to generate a GHZ entangled state of n photons in n microwave cavities (or resonators) via resonant interaction to a single superconducting qutrit. The deployment of a qutrit, instead of a qubit, as the coupler enables us to use resonant interactions exclusively for all qutrit-cavity and qutrit-pulse operations. This unique approach significantly shortens the time of operation which is advantageous to reducing the adverse effects of qutrit decoherence and cavity decay on fidelity of the protocol. Furthermore, the protocol involves no measurement on either the state of qutrit or cavity photons. We also show that the protocol can be generalized to other systems by replacing the superconducting qutrit coupler with different types of physical qutrit, such as an atom in the case of cavity QED, to accomplish the same task.

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