Solid-State Qubits with Current-Controlled Coupling

Superconducting circuits are promising candidates for constructing quantum bits (qubits) in a quantum computer; single-qubit operations are now routine 1,2 , and several examples 3,4,5,6,7,8,9 of two qubit interactions and gates having been demonstrated. These experiments show that two nearby qubits can be readily coupled with local interactions. Performing gates between an arbitrary pair of distant qubits is highly desirable for any quantum computer architecture, but has not yet been demonstrated. An efficient way to achieve this goal is to couple the qubits to a quantum bus, which distributes quantum information among the qubits. Here we show the implementation of such a quantum bus, using microwave photons confined in a transmission line cavity, to couple two superconducting qubits on opposite sides of a chip. The interaction is mediated by the exchange of virtual rather than real photons, avoiding cavity induced loss. Using fast control of the qubits to switch the coupling effectively on and off, we demonstrate coherent transfer of quantum states between the qubits. The cavity is also used to perform multiplexed control and measurement of the qubit states. This approach can be expanded to more than two qubits, and is an attractive architecture for quantum information processing on a chip.There are several physical systems in which one could realize a quantum bus. A particular example is trapped ions 10,11 in which a variety of quantum operations and algorithms have been performed using the quantized motion of the ions (phonons) as the bus. Photons are another natural candidate as a carrier of quantum information 12,13 , because they are highly coherent and can mediate interactions between distant objects. To create a photon bus, it is helpful to utilize the increased interaction strength provided by the techniques of cavity quantum electrodynamics, where an atom is coupled to a single cavity mode. In the strong coupling limit 14 the interaction is coherent, permitting the transfer of quantum information between the atom and the photon. Entanglement between atoms has been demonstrated with Rydberg atom cavity QED 15,16,17 . Circuit QED 18 is a realization of the physics of cavity QED with superconducting qubits coupled to a microwave cavity on a chip. Previous circuit QED experiments with single qubits have achieved 19 the strong coupling limit and have demonstrated 20 the transfer of quantum information from qubit to photon. Here we perform a circuit QED experiment with two qubits strongly coupled to a cavity, and demonstrate a coherent, non-local coupling between the qubits via this bus.Operations with multiple superconducting qubits have been performed and are a subject of current research. The first solid-state quantum gate has been demonstrated with charge qubits 3 . For flux qubits, two-qubit coupling 5 and a controllable coupling mechanism have been realized 7,8,9 . Two phase qubits have also been successfully coupled 4 and the entanglement between them has been observed 6 . All of these interactions h...

show abstract

“…

…”

mentioning

confidence: 99%

Coupling superconducting qubits via a cavity bus

Majer

Chow

Gambetta

et al. 2007

Nature

1,292

1,276

View full text Add to dashboard Cite

show abstract

“…5 We also considered two more models: ͑i͒ For N qubits inductively coupled without any connecting loop, multiplequbit interactions are intrinsically involved but their strengths are very weak, as for instance of N =4, J zzzz ͑4͒ Ϸ 10 −6 J zz00 ͑2͒ in the parameters of Ref. 12. If the two-qubit interactions are much stronger than other multiple-qubit interactions, H N Ϸ͚ iϽj H 2 ͑ij͒ .…”

Section: ͑10͒mentioning

confidence: 99%

“…Especially, coherent manipulation of quantum states in tunable superconducting devices has enabled to demonstrate macroscopic qubits [6][7][8] and entangled states of qubits. [9][10][11] Experimentally, it has been shown that, in terms of pseudospins, different types of exchange interactions between two artificial spins such as an Ising interaction for charge qubits 9 and flux qubits 10,12 and an XY interaction for phase qubits 11 can be realized and controlled by the system parameters. Although different types of solid-state qubit systems have revealed such artificial-spin exchange interactions, multiple artificial-spin interactions have not been demonstrated yet.…”

mentioning

confidence: 99%

See 1 more Smart Citation

Macroscopic many-qubit interactions in superconducting flux qubits

Cho¹,

Kim²

2008

Phys. Rev. B

View full text Add to dashboard Cite

Superconducting flux qubits are considered to investigate macroscopic many-qubit interactions. Many-qubit states based on current states can be manipulated through the current-phase relation in each superconducting loop. For flux qubit systems comprised of N-qubit loops, a general expression of low-energy Hamiltonian is presented in terms of low-energy levels of qubits and macroscopic quantum tunnelings between the many-qubit states. Many-qubit interactions classified by Ising-type or tunnel exchange interactions can be observable experimentally. Flux qubit systems can provide various artificial-spin systems to study many-body systems that cannot be found naturally. DOI: 10.1103/PhysRevB.77.212506 PACS number͑s͒: 74.50.ϩr, 03.67.Lx, 85.25.Cp It is believed that electrons are interacting in a pair. The interaction is called two-body interaction. Understanding the many-electron effects is one of the most important researches in condensed-matter physics. Normally, rich many-electron physics has been revealed by the two-body interactions of spin pairs in solid-state materials. In a strongly correlated electronic system, however, a low-energy Hamiltonian can involve more than three spin interactions. 1-4 Such multiplespin interactions are known to play a significant role in strongly correlated systems. Some examples include the magnetism of solid 3 He, the high T c superconductivity, and so on. 2,3 Moreover, it is well known theoretically that higher dimensional systems can be mapped to the multiple-spin interaction Hamiltonian of one-dimensional chain unlikely found naturally. 5 The last decade has seen rapidly developing advanced material technologies that make it possible to investigate previously inaccessible quantum systems for quantum information and computation in solid-state systems. Especially, coherent manipulation of quantum states in tunable superconducting devices has enabled to demonstrate macroscopic qubits 6-8 and entangled states of qubits. 9-11 Experimentally, it has been shown that, in terms of pseudospins, different types of exchange interactions between two artificial spins such as an Ising interaction for charge qubits 9 and flux qubits 10,12 and an XY interaction for phase qubits 11 can be realized and controlled by the system parameters. Although different types of solid-state qubit systems have revealed such artificial-spin exchange interactions, multiple artificial-spin interactions have not been demonstrated yet. This Brief Report aims to discuss, in a general framework, how artificial-multiple-spin interactions are possible and realizable in superconducting qubit systems. Flux qubit systems are shown to have an intrinsic property which is multiple artificial-spin interactions. Moreover, controllable system parameters in the flux qubit systems enable to create various types of artificial-spin systems even though a flux qubit system is fabricated experimentally. Then, the manmade superconducting structures of flux qubits can offer experimental simulators for many-body physics in associat...

show abstract

“…Superconducting qubits utilize charge [5][6][7] or flux [8] degrees of freedom, or energy levels quantization in a single current-biased Josephson junction [9,10]. Inter-qubit coupling [15][16][17][18][19][20] and also quantum logic gates [21][22][23] have been reported later. Further progress in the field slowed down due to obvious decoherence issues that are still to be overcome in order to implement a working quantum computer.…”

mentioning

confidence: 99%

Josephson charge qubits: a brief review

Pashkin

Astafiev

Yamamoto

et al. 2009

Quantum Inf Process

View full text Add to dashboard Cite

The field of solid-state quantum computation is expanding rapidly initiated by our original charge qubit demonstrations. Various types of solid-state qubits are being studied, and their coherent properties are improving. The goal of this review is to summarize achievements on Josephson charge qubits. We cover the results obtained in our joint group of NEC Nano Electronics Research Laboratories and RIKEN Advanced Science Institute, also referring to the works done by other groups. Starting from a short introduction, we describe the principle of the Josephson charge qubit, its manipulation and readout. We proceed with coupling of two charge qubits and implementation of a logic gate. We also discuss decoherence issues. Finally, we show how a charge qubit can be used as an artificial atom coupled to a resonator to demonstrate lasing action.

show abstract

Solid-State Qubits with Current-Controlled Coupling

Cited by 206 publications

References 24 publications

Coupling superconducting qubits via a cavity bus

Coupling superconducting qubits via a cavity bus

Macroscopic many-qubit interactions in superconducting flux qubits

Josephson charge qubits: a brief review

Contact Info

Product

Resources

About