### 62755 results for qubit oscillator frequency

Contributors: Grajcar, M., Izmalkov, A., Il'ichev, E., Wagner, Th., Oukhanski, N., Huebner, U., May, T., Zhilyaev, I., Hoenig, H. E., Greenberg, Ya. S.

Date: 2003-03-31

**frequency** ω T . Then both amplitude v and phase shift χ (with respect...**qubit**, inductively coupled to a Nb LC tank circuit. The resonant properties...**the** **qubit** vs external flux. The dashed lines represent **the** classical potential...probing field to **the** **qubit**, and detects its response....**qubit**, which changes drastically as its flux states pass through degeneracy... **qubit** temperature has been verified [Fig. fig:Temp_dep(b)] to be **the**...**3JJ** **qubit**....** qubit’s** quantum properties, without using spectroscopy. In a range 50 ...

**oscillator**are sensitive to the effective susceptibility (or inductance...

**qubit**anticross [Fig. fig:schem(a)], with a gap of 2 Δ . Increasing ...

**qubit**states. Thus, the tank both applies the probing field to the

**qubit**...

**frequency**due to the change of the effective

**qubit**inductance by the tank...

**the**

**qubit**can adiabatically transform from Ψ l to Ψ r , staying in

**the**...

**qubit**...

**b**) Phase

**qubit**coupled to a tank circuit....

**qubit**vs external flux. The dashed lines represent the classical potential...saturation of

**the**effective

**qubit**temperature at 30 mK. (c) Full dip width...

**qubit**....

**qubit**temperature at 30 mK. (c) Full dip width at half the maximum amplitude...

**qubit**coupled to a tank circuit. ... We have observed signatures of resonant tunneling in an Al three-junction

**qubit**, inductively coupled to a Nb LC tank circuit. The resonant properties of the tank

**oscillator**are sensitive to the effective susceptibility (or inductance) of the

**qubit**, which changes drastically as its flux states pass through degeneracy. The tunneling amplitude is estimated from the data. We find good agreement with the theoretical predictions in the regime of their validity.

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Contributors: Fedorov, Kirill G., Shcherbakova, Anastasia V., Schäfer, Roland, Ustinov, Alexey V.

Date: 2013-01-22

flux qubit....through** the **qubit corresponds to** the **changing of** the **persistent currents i...embracing a flux qubit, as shown in Fig. AJJ+Qubit. The current induced...the** flux** qubit with a coupling loop (yellow loop) and control line (green...**frequency** versus magnetic flux through the **qubit** corresponds to the changing... the qubit corresponds to** the **changing of** the **persistent currents in the...**oscillations**, we have performed systematic measurements of the dependence...**frequency** deviation from equilibrium δ ν / ν 0 of the fluxon **oscillation**...**qubit** as a current dipole to the annular junction, we detect periodic ...the** flux** qubit loop....the flux qubit....**oscillation** **frequency** from the unperturbed case δ ν = ν μ - ν 0 , where...**qubit**...**qubit**, **qubit** readout...**qubit**. The time delay of the fluxon can be detected as a **frequency** shift...**oscillation** **frequency** due to the coupling to the flux **qubit**. Every point...current in** the **flux qubit. Thus, the persistent current in** the **qubit manifests...flux qubit. Every point consists of 100 averages. Bias current was set...**frequency** versus bias current. Black line shows the result of perturbation...**oscillation** **frequency** for μ = 0 . Black line in Fig. FD shows the dependence...flux qubit versus magnetic frustration (black line). Red line shows the...**qubits** by using ballistic Josephson vortices are reported. We measured...**qubit**. We found that the scattering of a fluxon on a current dipole can...**oscillation** **frequency** versus magnetic flux through the **qubit**. We found...**qubit** loop....**qubit**. ... Experiments towards realizing a readout of superconducting **qubits** by using ballistic Josephson vortices are reported. We measured the microwave radiation induced by a fluxon moving in an annular Josephson junction. By coupling a flux **qubit** as a current dipole to the annular junction, we detect periodic variations of the fluxon's **oscillation** **frequency** versus magnetic flux through the **qubit**. We found that the scattering of a fluxon on a current dipole can lead to the acceleration of a fluxon regardless of a dipole polarity. We use the perturbation theory and numerical simulations of the perturbed sine-Gordon equation to analyze our results.

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Contributors: Xia, K., Macovei, M., Evers, J., Keitel, C. H.

Date: 2008-10-14

**qubits** are non-degenerate, and only afterwards render the two **qubits** degenerate...**qubits** via dynamic control of the transition frequencies...**oscillates** at twice the **frequency** of the population **oscillation**, since...**qubit** transition frequencies via the external bias flux in order to maximize...**in **the degenerate two-qubit system of about F = 0.94 is achieved. Finally... flux qubits interacting with each other through their mutual inductance...**qubit** transition **frequencies** around the optimum point. In the figure, ...the two qubits have a frequency difference Δ t = 0 = Δ 0 = 18 γ 0 . Applying...**oscillators**. As our main result, we achieve controlled robust creation...**qubits** interacting with each other through their mutual inductance and...**frequency** Ω 0 = 15 γ 0 and detuning δ = 0 , the symmetric state | s reaches...**frequency** and detuning required for SCRAP....two-**qubit** system....the two qubits are non-degenerate, and only afterwards render the two ...**qubit** transition **frequencies** via the external bias flux in order to maximize...control the qubit transition frequencies around the optimum point. In ...**oscillators**. We present different schemes using continuous-wave control...flux qubits coupled to each other through their mutual inductance M ...The two-qubit Hamiltonian H Q **in **two-level approximation and rotating ...that the two qubits become degenerate, Δ γ 0 t ≥ 160 = 0 . It can be seen...The two qubit transition frequencies are adjusted via time-dependent bias...**oscillate** between | a and | s due to the applied field. This **oscillation**...**oscillations** as a function of δ 0 . The maximum concurrence C is larger...**qubit** transition **frequencies** are adjusted via time-dependent bias fluxes...**qubits** have a **frequency** difference Δ t = 0 = Δ 0 = 18 γ 0 . Applying a...**oscillations** at **frequency** 2 2 Ω 0 , while the amplitude of the subsequent...**qubits** are operated around the optimum point, and decoherence is modelled ... Coherent control and the creation of entangled states are discussed in a system of two superconducting flux **qubits** interacting with each other through their mutual inductance and identically coupling to a reservoir of harmonic **oscillators**. We present different schemes using continuous-wave control fields or Stark-chirped rapid adiabatic passages, both of which rely on a dynamic control of the **qubit** transition **frequencies** via the external bias flux in order to maximize the fidelity of the target states. For comparison, also special area pulse schemes are discussed. The **qubits** are operated around the optimum point, and decoherence is modelled via a bath of harmonic **oscillators**. As our main result, we achieve controlled robust creation of different Bell states consisting of the collective ground and excited state of the two-**qubit** system.

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Contributors: Liberti, G., Zaffino, R. L., Piperno, F., Plastina, F.

Date: 2005-11-21

**qubit** is coupled to a single **oscillator** mode. 99 weiss U. Weiss, Quantum...**frequency** and the level asymmetry of the **qubit**. This is done in the adiabatic...**qubit**. This is done in the adiabatic regime in which the time evolution...of a qubit with an ohmic environment was numerically analyzed. It turns...of the **qubit** tunnelling amplitude D . One can appreciate that the result...**oscillator** in the lower adiabatic potential, for D = 10 and α = 2 and ...**qubit** is much faster than the oscillator one. Within the adiabatic approximation...**oscillator** defined in Eq. ( due1), centered in Q = ± Q 0 , respectively...**qubit** ( W = D = 0 ) would have given a pair of independent parabolas instead...the qubit is coupled to a single oscillator mode....**qubit** tunnelling amplitude D . One can appreciate that the result of Eq...**qubit** strongly interacting with an oscillator mode, as a function of the...asymmetry in the qubit Hamiltonian. As mentioned in section sect2 above...**qubit** coupled to a resonator in the adiabatic regime...**qubit** and the environmental **oscillator**. Unfortunately, the coupling strength...to the reduced qubit state. For example, for a large enough interaction...**oscillator** localizes in one of the wells of its effective potential and...**qubit** is much faster than the **oscillator** one. Within the adiabatic approximation...the qubit and the environmental oscillator. Unfortunately, the coupling...**qubit** strongly interacting with an **oscillator** mode, as a function of the ... We discuss the ground state entanglement of a bi-partite system, composed by a **qubit** strongly interacting with an **oscillator** mode, as a function of the coupling strenght, the transition **frequency** and the level asymmetry of the **qubit**. This is done in the adiabatic regime in which the time evolution of the **qubit** is much faster than the **oscillator** one. Within the adiabatic approximation, we obtain a complete characterization of the ground state properties of the system and of its entanglement content.

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Contributors: Rosenband, Till

Date: 2012-03-01

**oscillator** noise. In this context the squeezed states discussed by Andr...**qubits**, compared to the standard quantum limit (SQL). The most stable ...**qubits**, which are assumed not to decohere with one another....**frequency** corrections are φ E s t / 2 π T . Shaded in the background is...**qubits**, the protocol of Bu...**qubits** performance matches the analytical protocols. In the simulations...**qubits** can reduce clock instability, although the GHZ states yield no...**qubits** are required to improve upon the SQL by a factor of two....15 qubits, and improve upon the SQL variance by a factor of N -1 / 3 ....**oscillator** noise has an Allan deviation of 1 Hz....more qubits, the protocol of Bu...**qubits**, and improve upon the SQL variance by a factor of N -1 / 3 . For...**frequency** variance of the clock extrapolated to 1 second. For long-term...**frequency** is repeatedly corrected, based on projective measurements of...**qubits** yields improved clock stability compared to Ramsey spectroscopy...more qubits can reduce clock instability, although the GHZ states yield...few-**qubit** clock protocols...**oscillator** decoheres due to flicker-**frequency** (1/f) noise. The **oscillator** ... The stability of several clock protocols based on 2 to 20 entangled atoms is evaluated numerically by a simulation that includes the effect of decoherence due to classical **oscillator** noise. In this context the squeezed states discussed by Andr\'{e}, S{\o}rensen and Lukin [PRL 92, 239801 (2004)] offer reduced instability compared to clocks based on Ramsey's protocol with unentangled atoms. When more than 15 atoms are simulated, the protocol of Bu\v{z}ek, Derka and Massar [PRL 82, 2207 (1999)] has lower instability. A large-scale numerical search for optimal clock protocols with two to eight **qubits** yields improved clock stability compared to Ramsey spectroscopy, and for two to three **qubits** performance matches the analytical protocols. In the simulations, a laser local **oscillator** decoheres due to flicker-**frequency** (1/f) noise. The **oscillator** **frequency** is repeatedly corrected, based on projective measurements of the **qubits**, which are assumed not to decohere with one another.

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Contributors: Oxtoby, Neil P., Gambetta, Jay, Wiseman, H. M.

Date: 2007-06-24

**qubit**, is used to damp a classical oscillator circuit. The resulting realistic...**frequency** (rf) weak measurements where a low-transparency quantum point... the **qubit** electron, denoted by E 1 and E 0 for the near and far dot, ...low-**frequency** (dc) weak measurements. In this paper we extend realistic...**oscillator** circuit to be a QPC (see Fig. fig:dqdqpc for details). Measurement...**qubit**. A schematic of the isolated DQD and capacitively coupled QPC is...**qubit**. The charge basis states are denoted | 0 and | 1 (see Fig. fig:...**qubit** coupled to a classical L C **oscillator** with inductance L and capacitance...**qubits** is important for quantum computation, particularly for the purposes...radio-**frequency** point contact), with two benefits over the SET — lower...**qubit** using a radio-frequency quantum point contact including experimental...**frequency** is the same as the signal of interest (or very slightly detuned...**qubit**. The rf+dc mode of operation is considered. Here the QPC is biased...charge **qubit** coupled to a classical L C oscillator with inductance L and...**qubit**, is used to damp a classical **oscillator** circuit. The resulting realistic... **qubit** coupled to a classical L C oscillator with inductance L and capacitance...low-**frequency** beats due to mixing the signal with the LO are easily detected...charge-**qubit** detector, that may nevertheless be higher than the dc-QPC...**qubit** and capacitively coupled low-transparency QPC between source (S)...**oscillator**, L O , and then measured. fig:rfcircuit...**oscillator** (relative to the QPC), where the **oscillator** slaves to the **qubit**... **qubit**. The charge basis states are denoted | 0 and | 1 (see Fig. fig ... The extension of quantum trajectory theory to incorporate realistic imperfections in the measurement of solid-state **qubits** is important for quantum computation, particularly for the purposes of state preparation and error-correction as well as for readout of computations. Previously this has been achieved for low-**frequency** (dc) weak measurements. In this paper we extend realistic quantum trajectory theory to include radio **frequency** (rf) weak measurements where a low-transparency quantum point contact (QPC), coupled to a charge **qubit**, is used to damp a classical **oscillator** circuit. The resulting realistic quantum trajectory equation must be solved numerically. We present an analytical result for the limit of large dissipation within the **oscillator** (relative to the QPC), where the **oscillator** slaves to the **qubit**. The rf+dc mode of operation is considered. Here the QPC is biased (dc) as well as subjected to a small-amplitude sinusoidal carrier signal (rf). The rf+dc QPC is shown to be a low-efficiency charge-**qubit** detector, that may nevertheless be higher than the dc-QPC (which is subject to 1/f noise).

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Contributors: Martijn Wubs, Sigmund Kohler, Peter Hänggi

Date: 2007-10-01

**qubit** may undergo Landau–Zener transitions due to its coupling to one ...a qubit coupled to two oscillators. Parameters: γ=0.25ℏv and Ω2=100ℏv,...**qubit**–oscillator entanglement, with state-of-the-art circuit QED as a ...**qubit** are well suited for the robust creation of entangled cavity states...**qubit** that is coupled to one **oscillator**. Starting in the ground state ...**qubit** coupled to one **oscillator**, far outside the RWA regime: γ=ℏΩ=0.25ℏv...**qubit** coupled to two cavities, we show that Landau–Zener sweeps of the...**oscillator** **frequencies**, both inside and outside the regime where a rotating-wave...**qubit** coupled to two **oscillators**. Parameters: γ=0.25ℏv, ℏΩ1=90ℏv, and ...case** the **qubit would be measured |↑〉.
...**oscillators**. We show that for a **qubit** coupled to one **oscillator**, Landau–Zener... the qubit–oscillator coupling γ. Parameters: γ=0.25ℏv and ℏΩ2=100ℏv, ...**qubit** coupled to one oscillator, Landau–Zener transitions can be used ...**oscillator** if the **qubit** would be measured in state |↓〉; the dash-dotted...**qubit** coupled to two **oscillators** with degenerate energies. Parameters:...**sweep** of a qubit coupled to two oscillators with degenerate energies. ...**qubit**–**oscillator** entanglement, with state-of-the-art circuit QED as a ...LZ **sweep** of a qubit coupled to two oscillators. Parameters: γ=0.25ℏv, ... A **qubit** may undergo Landau–Zener transitions due to its coupling to one or several quantum harmonic **oscillators**. We show that for a **qubit** coupled to one **oscillator**, Landau–Zener transitions can be used for single-photon generation and for the controllable creation of **qubit**–**oscillator** entanglement, with state-of-the-art circuit QED as a promising realization. Moreover, for a **qubit** coupled to two cavities, we show that Landau–Zener sweeps of the **qubit** are well suited for the robust creation of entangled cavity states, in particular symmetric Bell states, with the **qubit** acting as the entanglement mediator. At the heart of our proposals lies the calculation of the exact Landau–Zener transition probability for the **qubit**, by summing all orders of the corresponding series in time-dependent perturbation theory. This transition probability emerges to be independent of the **oscillator** **frequencies**, both inside and outside the regime where a rotating-wave approximation is valid.

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Contributors: Chiorescu, I., Bertet, P., Semba, K., Nakamura, Y., Harmans, C. J. P. M., Mooij, J. E.

Date: 2004-07-30

**oscillator**. We achieve generation and control of the entangled state by...**frequencies** are shown by the filled squares in b). b, Rabi **frequency**, .......**oscillations**: after a π pulse on the **qubit** resonance ( | 00 → | 10 ) we...flux **qubit** (the smallest loop closed by three junctions); the **qubit** to...**frequencies** indicated by peaks in the SQUID switching probability when...**qubit** - **oscillator** system for some given bias point. The blue and red ...**oscillations** of the coupled system....**oscillations** at the **qubit** symmetry point Δ = 5.9 GHz. a, Switching probability...**qubit** symmetry point Δ = 5.9 GHz. a, Switching probability as a function...**oscillator**, as demonstrated in ion/atom-trap experiments or cavity quantum...**qubit** (a two-level system) and a superconducting quantum interference ...**qubits**. Single-**qubit** operations, direct coupling between two **qubits**, and... the **qubit** transition. In the upper scan, the system is first excited ...through the **qubit** area away from the **qubit** symmetry point. Inset, energy...**qubit** coupled to a harmonic oscillator...Qub ... In the emerging field of quantum computation and quantum information, superconducting devices are promising candidates for the implementation of solid-state quantum bits or **qubits**. Single-**qubit** operations, direct coupling between two **qubits**, and the realization of a quantum gate have been reported. However, complex manipulation of entangled states - such as the coupling of a two-level system to a quantum harmonic **oscillator**, as demonstrated in ion/atom-trap experiments or cavity quantum electrodynamics - has yet to be achieved for superconducting devices. Here we demonstrate entanglement between a superconducting flux **qubit** (a two-level system) and a superconducting quantum interference device (SQUID). The latter provides the measurement system for detecting the quantum states; it is also an effective inductance that, in parallel with an external shunt capacitance, acts as a harmonic **oscillator**. We achieve generation and control of the entangled state by performing microwave spectroscopy and detecting the resultant Rabi **oscillations** of the coupled system.

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Contributors: Catelani, G., Schoelkopf, R. J., Devoret, M. H., Glazman, L. I.

Date: 2011-06-04

**qubit**, such as the transmon and phase **qubits**. We start with the the semiclassical...**ϕ** ̂ / 2 qubit-quasiparticle coupling in Eq. ( HTle) has a striking effect...**qubit** controlled by a magnetic flux, see Eq. ( Hphi). (b) Effective circuit...**qubit** biased at Φ e = Φ 0 / 2 with E J / E L = 10 . The horizontal lines...flux **qubit** biased at Φ e = Φ 0 / 2 with E J / E L = 10 . The horizontal...the flux qubit ground states | - and excited state | + are** the **lowest ...**qubit** sate. The results of Sec. sec:semi are valid for transitions between...**qubits**. The interaction of the **qubit** degree of freedom with the quasiparticles...**frequency** [cf. Eq. ( pl_fr)]...**qubit** frequency in the presence of quasiparticles....**frequency** is given by Eq. ( Gnn) with ϕ 0 = 0 and is independent of n ...**qubit** **frequency** in the presence of quasiparticles.... C , the qubit can be described by** the **effective circuit of Fig. fig1...**oscillations** of the energy levels are exponentially small, see Appendix...**qubit** resonant **frequency**. In the semiclassical regime of small E C , the... a **qubit** controlled by a magnetic flux, see Eq. ( Hphi). (b) Effective...**qubit** properties in devices such as the phase and flux **qubits**, the split...**the** **qubit** sate. The results of Sec. sec:semi are valid for transitions...**qubits**...**frequency** ω p , Eq. ( pl_fr)] and nearly degenerate levels whose energies...**qubit** decay rate induced by quasiparticles, and we study its dependence...**frequency** ω p , Eq. ( pl_fr), and give, for example, the rate Γ 1 0 . ...the flux quantum** the **qubit states | - , | + are respectively symmetric...anharmonic qubit, such as** the **transmon and **phase **qubits. We start with ... As low-loss non-linear elements, Josephson junctions are the building blocks of superconducting **qubits**. The interaction of the **qubit** degree of freedom with the quasiparticles tunneling through the junction represent an intrinsic relaxation mechanism. We develop a general theory for the **qubit** decay rate induced by quasiparticles, and we study its dependence on the magnetic flux used to tune the **qubit** properties in devices such as the phase and flux **qubits**, the split transmon, and the fluxonium. Our estimates for the decay rate apply to both thermal equilibrium and non-equilibrium quasiparticles. We propose measuring the rate in a split transmon to obtain information on the possible non-equilibrium quasiparticle distribution. We also derive expressions for the shift in **qubit** **frequency** in the presence of quasiparticles.

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Contributors: Zhirov, O. V., Shepelyansky, D. L.

Date: 2007-10-10

**qubit** coupled to a quantum dissipative driven oscillator (resonator). ...**oscillator** with x = â + â / 2 , p = â - â / 2 i (left) and for **qubit** polarization...**frequency** of effective Rabi **oscillations** between quasi-degenerate levels...**oscillator** performs circle rotations in p x plane with **frequency** ω while...synchronization of qubit with radiation suppression **at** qubit frequency...**qubit** radiation spectrum with appearance of narrow lines corresponding...phenomenon of qubit synchronization is illustrated in a more clear way...the **qubit** polarization phase φ vs. oscillator phase ϕ ( p / x = - tan ...**qubit** coupled to a driven dissipative oscillator...**qubit** exhibits tunneling between two orientations with a macroscopic change...**qubit** coupled to a driven **oscillator** with jumps between two metastable...**qubit** radiation ξ z t as function of driving power n p in presence of ...**qubit** rotations become synchronized with the oscillator phase. In the ...direction of qubit polarization also changes in a smooth but nontrivial...rescaled **qubit** frequency Ω / ω 0 for parameters of Fig. fig1; N f are...**qubit** **frequency** Ω / ω 0 for parameters of Fig. fig1; N f are computed...Bistability of **qubit** coupled to a driven oscillator with jumps between...**qubit** polarization phase φ vs. **oscillator** phase ϕ ( p / x = - tan ϕ ) ...shows the **qubit** polarization vector components ξ x (blue/black) and ξ ...**qubit** rotations become synchronized with the **oscillator** phase. In the ...**qubit** with radiation suppression at **qubit** **frequency** Ω = 1.2 ω 0 and appearance...**oscillator** in two metastable states on the driving **frequency** ω (average...**qubit** coupled to a quantum dissipative driven **oscillator** (resonator). ...state** the **degree of qubit polarization ξ = | ξ → | is very close to unity s ... We study numerically the behavior of **qubit** coupled to a quantum dissipative driven **oscillator** (resonator). Above a critical coupling strength the **qubit** rotations become synchronized with the **oscillator** phase. In the synchronized regime, at certain parameters, the **qubit** exhibits tunneling between two orientations with a macroscopic change of number of photons in the resonator. The life times in these metastable states can be enormously large. The synchronization leads to a drastic change of **qubit** radiation spectrum with appearance of narrow lines corresponding to recently observed single artificial-atom lasing [O. Astafiev {\it et al.} Nature {\bf 449}, 588 (2007)].

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