We propose a fast and simple scheme for generating NOON states of photons in two superconducting resonators by using a single superconducting phase qutrit. Because only one superconductingqutrit and two resonators are used, the experimental setup for this sheme 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.
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 proposaldoes 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.
The generation and control of quantum states of spatially-separated qubits distributed in different cavities constitute fundamental tasks in cavity quantum electrodynamics. An interestingquestion 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.
We discuss how to generate entangled coherent states of four extrm{microwave} resonators extrm{(a.k.a. cavities)} coupled by a superconducting qubit. We also show extrm{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.
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 couplerqubit. The quantum states to be exchanged or transferred can be arbitrary pure or mixed states. 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. The method can be generalized to other systems by using different types of physical qubit as a coupler to accomplish the same task.
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 needof 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.
We present a way to realize quantum information transfer with superconducting
flux qubits coupled to a cavity. Because only resonant qubit-cavity interaction
and resonant qubit-pulseinteraction are applied, the information transfer can
be performed much faster, when compared with the previous proposals. This
proposal does not require adjustment of the qubit level spacings during the
operation. Moreover, neither uniformity in the device parameters nor exact
placement of qubits in the cavity is needed by this proposal.