Papers by vladimir manucharyan
Superconducting order in a sufficiently narrow and infinitely long wire is destroyed at zero temp... more Superconducting order in a sufficiently narrow and infinitely long wire is destroyed at zero temperature by quantum fluctuations, which induce $2\pi$ slips of the phase of the order parameter. However, in a finite-length wire coherent quantum phase-slips would manifest themselves simply as shifts of energy levels in the excitations spectrum of an electrical circuit incorporating this wire. The higher the phase-slips probability amplitude, the larger are the shifts. Phase-slips occurring at different locations along the wire interfere with each other. Due to the Aharonov-Casher effect, the resulting full amplitude of a phase-slip depends on the offset charges surrounding the wire. Slow temporal fluctuations of the offset charges make the phase-slips amplitudes random functions of time, and therefore turn energy levels shifts into linewidths. We experimentally observed this effect on a long Josephson junction array acting as a "slippery" wire. The slip-induced linewidths, despite being only of order 100 kHz, were resolved from the flux-dependent dephasing of the fluxonium qubit.
Physical Review B, 2007
A Josephson tunnel junction which is rf driven near a dynamical bifurcation point can amplify qua... more A Josephson tunnel junction which is rf driven near a dynamical bifurcation point can amplify quantum signals. However, the bifurcation point will exist robustly only if the electrodynamic environment of the junction meets certain criteria. We develop a general formalism for dealing with the nonlinear dynamics of a Josephson junction embedded in an arbitrary microwave circuit. We find sufficient conditions for the existence of the bifurcation regime: ͑a͒ the embedding impedance of the junction needs to present a resonance at a particular frequency R , with the quality factor Q of the resonance and the participation ratio p of the junction satisfying Qp ӷ 1, and ͑b͒ the drive frequency should be low frequency detuned away from R by more than ͱ 3 R / ͑2Q͒.
Nature Physics, 2010
Amplifiers are crucial in every experiment carrying out a very sensitive measurement. However, th... more Amplifiers are crucial in every experiment carrying out a very sensitive measurement. However, they always degrade the information by adding noise. Quantum mechanics puts a limit on how small this degradation can be. Theoretically, the minimum noise energy added by a phase preserving amplifier to the signal it processes amounts at least to half a photon at the signal frequency ( 1 2h ω). In this article, we show that we can build a practical microwave device that fulfills the minimal requirements to reach the quantum limit. This is of importance for the readout of solid state qubits, and more generally, for the measurement of very weak signals in various areas of science. We also discuss how this device can be the basic buiding block for a variety of practical applications such as amplification, noiseless frequency conversion, dynamic cooling and production of entangled signal pairs.
We have developed and operated a new type of phase preserving parametric amplifier, the Josephson... more We have developed and operated a new type of phase preserving parametric amplifier, the Josephson Parametric Converter, which approaches the quantum limit. Our device consists of two microwave resonators coupled to each other through a Josephson Ring Modulator. This latter element resembles a DC-SQUID, but has four junctions, and four active current modes instead of two. A pump line is non-resonantly coupled to one of the modes of the ring while the signal and idler are serviced by two others and are tuned in the band of the resonators. The fourth mode, which is the dc superconducting circulating current in the ring, is biased with half a flux quantum. Our design ensures that the non-linearity presented by the Ring Modulator is pure and involves the minimal number of modes, thus placing the JPC very close to the ideal non-degenerate parametric amplifier. This is supported by recent results on the amplification and frequency conversion operations. Furthermore, measurements of the noise temperature with an auto-calibrated source based on a nanowire in the hot electron regime will be presented. In combination with correlation measurements of the noise at the signal and idler ports, these results show that the JPC can perform two-mode squeezing of quantum noise.
We present Quantum Non-Demolition (QND) measurements of a Fluxonium qubit, which utilizes a Josep... more We present Quantum Non-Demolition (QND) measurements of a Fluxonium qubit, which utilizes a Josephson junction array inductance to shunt the junction of a Cooper-pair box qubit. The Cooper-pair box is coupled capacitively to a readout cavity, which assesses the state of the qubit through a dispersive shift of the cavity frequency. By sending a microwave pulse at the cavity frequency and monitoring the phase of the reflected signal, a direct measurement of the qubit state is acquired after a preparation pulse. We will discuss the QND nature of the measurement, the use of sideband transitions for preparing the qubit state, and the prospect for single shot QND readout.
Physical Review B, 2007
Dispersive readouts for superconducting qubits have the advantage of speed and minimal invasivene... more Dispersive readouts for superconducting qubits have the advantage of speed and minimal invasiveness. We have developed such an amplifier, the Cavity Bifurcation Amplifier (CBA) [10], and applied it to the readout of the quantronium qubit [2]. It consists of a Josephson junction embedded in a microwave on-chip resonator. In contrast with the Josephson bifurcation amplifier [17], which has an on-chip capacitor shunting a junction, the resonator is based on a simple coplanar waveguide imposing a pre-determined frequency and whose other RF characteristics like the quality factor are easily controlled and optimized. Under proper microwave irradiation conditions, the CBA has two metastable states. Which state is adopted by the CBA depends on the state of a quantronium qubit coupled to the CBA's junction. Due to the MHz repetition rate and large signal to noise ratio we can show directly that the coherence is limited by 1/f gate charge noise when biased at the sweet spot - a point insensitive to first order gate charge fluctuations. This architecture lends itself to scalable quantum computing using a multi-resonator chip with multiplexed readouts.
We present the design and data from a new, strongly coupled superconducting qubit based on Joseph... more We present the design and data from a new, strongly coupled superconducting qubit based on Josephson junctions and a strictly 1-dimensional distributed element geometry that operates in the Transmon regime. A cavity bifurcation amplifier is used to read the state of the qubit. The same circuit also supports a linear dispersive readout, which enables direct comparison between the latching and dispersive scheme. Most recent results will be discussed.
Recent progress in solid state quantum information processing has stimulated the search for ultra... more Recent progress in solid state quantum information processing has stimulated the search for ultra-low-noise amplifiers and frequency converters in the microwave frequency range, which could attain the ultimate limit imposed by quantum mechanics. In this article, we report the first realization of an intrinsically phase-preserving, non-degenerate superconducting parametric amplifier, a so far missing component. It is based on the Josephson ring modulator, which consists of four junctions in a Wheatstone bridge configuration. The device symmetry greatly enhances the purity of the amplification process and simplifies both its operation and analysis. The measured characteristics of the amplifier in terms of gain and bandwidth are in good agreement with analytical predictions. Using a newly developed noise source, we also show that our device operates within a factor of three of the quantum limit. This development opens new applications in the area of quantum analog signal processing.
We present a cryoelectronics sample holder design which provides a compact perpendicular coaxial ... more We present a cryoelectronics sample holder design which provides a compact perpendicular coaxial to microstrip transition with a return loss better than 14dB and insertion loss less than 2dB from DC-20GHz, and port isolation better than 60dB up to 8GHz and 40dB up to 10GHz. The design fully encloses the sample, provides good electrical and thermal contact to the sample, and is straightforward to construct.
Quantum Mechanics puts a limit on how small the degradation of information passing through a phas... more Quantum Mechanics puts a limit on how small the degradation of information passing through a phase preserving amplifier can be. It is known theoretically that the minimum noise added by the amplifier to the signal amounts at least to half a photon at the signal frequency. Is it possible to construct a practical amplifier working at microwave frequencies that would reach this quantum limit? We have developed a new device aiming at answering this question, which is of practical importance for the readout of solid state qubits, and more generally, for the measurement of very weak signals in various areas of science. The device is based on a ring of four Josephson junctions which connects two microwave resonators corresponding to the signal and idler modes. It can be operated both as an amplifier and a frequency converter. Theoretical aspects and experimental results will be presented.
Dispersive readouts for superconducting qubits have the advantage of speed and minimal invasivene... more Dispersive readouts for superconducting qubits have the advantage of speed and minimal invasiveness. We have developed a new type of dispersive bifurcating amplifier, which consists of a Josephson junction imbedded in a microwave on-chip resonator. In contrast with the Josephson bifurcation amplifier [1,2,3], which has an on-chip capacitor shunting a junction, the resonator is based on a simple coplanar waveguide imposing a pre-determined frequency and whose other RF characteristics like the quality factor are easily controlled and optimized. Furthermore, readout frequencies ranging from 1 to 10GHz have been realized. Under proper microwave irradiation conditions, the resonator has two metastable states. Which state is adopted by the resonator depends on the state of a qubit coupled to the readout junction. We present the characterization of the Cavity Bifurcation Amplifier and demonstrate its application as a readout for the Quantronium qubit. [1] I. Siddiqi et al. Phys. Rev. Lett 93, 207002 (2004) [2] I. Siddiqi et al. Phys. Rev. Lett. 94, 027005 (2005) [3] I. Siddiqi et al. Phys. Rev. B. 73, 0054510 (2006)
We propose a new superconducting qubit design, where a small Josephson junction is inserted in th... more We propose a new superconducting qubit design, where a small Josephson junction is inserted in the central conductor of a coplanar waveguide resonator. In this distributed element design, the resonator provides a negative reactance for the junction, which modifies the charging energy EC of the junction and places the qubit far in the ``Transmon regime'', EJEC, where EJ is the Josephson energy of the junction. We will discuss design details and show preliminary fabrication and measurement results.
Fluxonium is a highly anharmonic artificial atom, which utilizes an inductance formed by an array... more Fluxonium is a highly anharmonic artificial atom, which utilizes an inductance formed by an array of large Josephson junctions to shunt the junction of a Cooper-pair box. The first excited state transition frequency is widely tunable with flux, yet can be read out over the entire five octave range due to interactions of the 2nd excited state with the readout cavity, enabling a dispersive readout. We present T1 times of several fluxonium samples over the full range of flux dependent transition energies. By mapping out the qubit lifetimes we are able to distinguish between the contributions due to the Purcell effect and quantify dissipation internal to the qubit. With this understanding, we can design a qubit with minimized contribution from internal losses, which should push lifetimes further into the tens of microseconds. [1] V. E. Manucharyan et al., Science 326, 113 (2009).
Thirty years ago, A. J. Leggett proposed that a superconducting loop interrupted by a Josephson t... more Thirty years ago, A. J. Leggett proposed that a superconducting loop interrupted by a Josephson tunnel junction might display a coherent oscillation between trapping and detrapping of a single flux quantum. This phenomenon of reversible quantum tunneling between two classically separable states of identical energy, known as Macroscopic Quantum Coherence (MQC), is regarded crucial for precise tests of whether macroscopic systems such as circuits fully obey quantum mechanics. We report time-domain observation of MQC oscillations at sub-GHz frequency and quality factor larger than 500. Two major innovations have been introduced to achieve this result: (i) the loop inductance is 10,000 larger than in previous experiments, allowing the junction to enter the charging regime and (ii) a novel microwave cavity-assisted readout scheme free of Purcell effect. Contrary to expectations, we find that the MQC transition could be the basis of a superconducting qubit of improved coherence and readout fidelity.
Nature, 2010
Recent progress in solid state quantum information processing has stimulated the search for ultra... more Recent progress in solid state quantum information processing has stimulated the search for ultralow-noise amplifiers and frequency converters in the microwave frequency range, which could attain the ultimate limit imposed by quantum mechanics. In this article, we report the first realization of an intrinsically phase-preserving, non-degenerate superconducting parametric amplifier, a so far missing component. It is based on the Josephson ring modulator, which consists of four junctions in a Wheatstone bridge configuration. The device symmetry greatly enhances the purity of the amplification process and simplifies both its operation and analysis. The measured characteristics of the amplifier in terms of gain and bandwidth are in good agreement with analytical predictions.
Phase slips are events in which the phase across a superconducting wire changes by 2π. The therma... more Phase slips are events in which the phase across a superconducting wire changes by 2π. The thermally activated phase slips at high temperatures are well understood but the coherent phase slips caused by quantum fluctuations well below the critical temperature have, so far, eluded observation. We report new decoherence data for the fluxonium qubit [1] that provide evidence for coherent quantum phase slips across the qubit inductance, implemented with a long array of Josephson tunnel junctions. Coherent quantum phase slips result in broadening of the qubit transition frequency due to Aharonov-Casher interference of multiple phase slip paths (or flux tunneling through different junctions) encircling random offset charges on array islands [2]. [4pt] [1] V.E. Manucharyan et al., Science 326, 113 (2009).[0pt] [2] D. Ivanov et al., Phys. Rev. B 65, 024509 (2002).
Amplifiers are crucial in every experiment carrying out a very sensitive measurement. However, th... more Amplifiers are crucial in every experiment carrying out a very sensitive measurement. However, they always degrade the information by adding noise. Quantum mechanics puts a limit on how small this degradation can be. Theoretically, the minimum noise energy added by a phase preserving amplifier to the signal it processes amounts at least to half a photon at the signal frequency ( 1 2h ω). In this article, we show that we can build a practical microwave device that fulfills the minimal requirements to reach the quantum limit. This is of importance for the readout of solid state qubits, and more generally, for the measurement of very weak signals in various areas of science. We also discuss how this device can be the basic buiding block for a variety of practical applications such as amplification, noiseless frequency conversion, dynamic cooling and production of entangled signal pairs.
Science, 2009
The promise of single Cooper-pair quantum circuits based on tunnel junctions for metrology and qu... more The promise of single Cooper-pair quantum circuits based on tunnel junctions for metrology and quantum information applications is severely limited by the influence of offset charges: random, slowly drifting microscopic charges inherent in many solid-state systems. By shunting a small junction with the Josephson kinetic inductance of a series array of large-capacitance tunnel junctions, thereby ensuring that all superconducting islands are connected to the circuit by at least one large junction, we have realized a new superconducting artificial atom that is totally insensitive to offset charges. Yet its energy levels manifest the anharmonic structure associated with single Cooper-pair effects, a useful component for solid-state quantum computation.
We introduce a novel superconducting quantum electrical circuit where a small capacitance Josephs... more We introduce a novel superconducting quantum electrical circuit where a small capacitance Josephson tunnel junction is shunted by an array of larger junctions to form a loop. The loop is capacitively coupled to a microwave transmission line resonator in order to perform a dispersive readout of the qubit state. The low-lying energy states of such circuit belong to the microwave band and tune with magnetic flux threading the loop. Our circuit differs significantly from the well-established charge, flux and phase qubit circuits. Namely, while staying highly anharmonic, the energy spectrum is neither sensitive to the offset charges nor it is exponentially sensitive to the junction parameters or flux bias. We demonstrate experimentally strong coupling to the readout resonator, map the spectrum over wide range of bias fluxes and frequencies and observe coherence times in excess of one microsecond.
Several types of amplifiers are approaching the quantum limit, namely, the SQUID, the RF-SET (rad... more Several types of amplifiers are approaching the quantum limit, namely, the SQUID, the RF-SET (radio-frequency single electron transistor) and the QCP (quantum point contact). We investigate a new amplifier which harnesses the nonlinearity of a Josephson junction for parametric amplification. It consists of a Josephson junction placed in a high-quality on-chip superconducting cavity, pumped by microwave radiation. The high level of control over the environment provides a system which is well described by the simplest nonlinear oscillator formalism with no adjustable parameters. such that theoretical predictions can be compared with experimental results. The planar geometry of the device can accommodate operation over a wide range of frequencies, opening the possibility of a quantum limited amplifier for practical use. We present preliminary results on the performance of the amplifier and discuss the possibility of observing quantum noise squeezing.
Uploads
Papers by vladimir manucharyan