N. E. Frattini

Frequency-tunable Kerr-free three-wave mixing with a gradiometric SNAIL

  1. A. Miano,
  2. G. Liu,
  3. V. V. Sivak,
  4. N. E. Frattini,
  5. V. R. Joshi,
  6. W. Dai,
  7. L. Frunzio,
  8. and M. H. Devoret
Three-wave mixing is a key process in superconducting quantum information processing, being involved in quantum-limited amplification and parametric coupling between superconducting
cavities. These operations can be implemented by SNAIL-based devices that present a Kerr-free flux-bias point where unwanted parasitic effects such as Stark shift are suppressed. However, with a single flux-bias parameter, these circuits can only host one Kerr-free point, limiting the range of their applications. In this Letter, we demonstrate how to overcome this constraint with a gradiometric SNAIL, a doubly-flux biased superconducting circuit for which both effective inductance and Kerr coefficient can be independently tuned. Experimental data show the capability of the gradiometric SNAIL to suppress Kerr effect in a three-wave mixing parametric amplifier over a continuum of flux bias points corresponding to a 1.7 GHz range of operating frequencies.
arxiv pdf

A stabilized logical quantum bit encoded in grid states of a superconducting cavity

  1. P. Campagne-Ibarcq,
  2. A. Eickbusch,
  3. S. Touzard,
  4. E. Zalys-Geller,
  5. N. E. Frattini,
  6. V. V. Sivak,
  7. P. Reinhold,
  8. S. Puri,
  9. S. Shankar,
  10. R. J. Schoelkopf,
  11. L. Frunzio,
  12. M. Mirrahimi,
  13. and M.H. Devoret
The majority of quantum information tasks require error-corrected logical qubits whose coherence times are vastly longer than that of currently available physical qubits. Among the
many quantum error correction codes, bosonic codes are particularly attractive as they make use of a single quantum harmonic oscillator to encode a correctable qubit in a hardware-efficient manner. One such encoding, based on grid states of an oscillator, has the potential to protect a logical qubit against all major physical noise processes. By stroboscopically modulating the interaction of a superconducting microwave cavity with an ancillary transmon, we have successfully prepared and permanently stabilized these grid states. The lifetimes of the three Bloch vector components of the encoded qubit are enhanced by the application of this protocol, and agree with a theoretical estimate based on the measured imperfections of the experiment.
arxiv pdf

Bias-preserving gates with stabilized cat qubits

  1. Shruti Puri,
  2. Lucas St-Jean,
  3. Jonathan A. Gross,
  4. Alexander Grimm,
  5. N. E. Frattini,
  6. Pavithran S. Iyer,
  7. Anirudh Krishna,
  8. Steven Touzard,
  9. Liang Jiang,
  10. Alexandre Blais,
  11. Steven T. Flammia,
  12. and S. M. Girvin
The code capacity threshold for error correction using qubits which exhibit asymmetric or biased noise channels is known to be much higher than with qubits without such structured noise.However, it is unclear how much this improvement persists when realistic circuit level noise is taken into account. This is because implementations of gates which do not commute with the dominant error un-bias the noise channel. In particular, a native bias-preserving controlled-NOT (CX) gate, which is an essential ingredient of stabilizer codes, is not possible in strictly two-level systems. Here we overcome the challenge of implementing a bias-preserving CX gate by using stabilized cat qubits in driven nonlinear oscillators. The physical noise channel of this qubit is biased towards phase-flips, which increase linearly with the size of the cat, while bit-flips are exponentially suppressed with cat size. Remarkably, the error channel of this native CX gate between two such cat qubits is also dominated by phase-flips, while bit-flips remain exponentially suppressed. This CX gate relies on the topological phase that arises from the rotation of the cat qubit in phase space. The availability of bias-preserving CX gates opens a path towards fault-tolerant codes tailored to biased-noise cat qubits with high threshold and low overhead. As an example, we analyze a scheme for concatenated error correction using cat qubits. We find that the availability of CX gates with moderately sized cat qubits, having mean photon number <10, improves a rigorous lower bound on the fault-tolerance threshold by a factor of two and decreases the overhead in logical Clifford operations by a factor of 5. We expect these estimates to improve significantly with further optimization and with direct use of other codes such as topological codes tailored to biased noise.[/expand]
arxiv pdf

Kerr-free three-wave mixing in superconducting quantum circuits

  1. V. V. Sivak,
  2. N. E. Frattini,
  3. V. R. Joshi,
  4. A. Lingenfelter,
  5. S. Shankar,
  6. and M. H. Devoret
Quantum-limited Josephson parametric amplifiers are crucial components in circuit QED readout chains. The dynamic range of state-of-the-art parametric amplifiers is limited by signal-induced
Stark shifts that detune the amplifier from its operating point. Using a Superconducting Nonlinear Asymmetric Inductive eLement (SNAIL) as an active component, we show the ability to in situ tune the device flux and pump to a dressed Kerr-free operating point, which provides a 10-fold increase in the number of photons that can be processed by our amplifier, compared to the nominal working point. Our proposed and experimentally verified methodology of Kerr-free three-wave mixing can be extended to improve the dynamic range of other pumped operations in quantum superconducting circuits.
arxiv pdf

Experimental implementation of a Raman-assisted six-quanta process

  1. S. O. Mundhada,
  2. A. Grimm,
  3. J. Venkatraman,
  4. Z.K. Minev,
  5. S. Touzard,
  6. N. E. Frattini,
  7. V. V. Sivak,
  8. K. Sliwa,
  9. P. Reinhold,
  10. S. Shankar,
  11. M. Mirrahimi,
  12. and M.H. Devoret
Fault tolerant quantum information processing requires specific nonlinear interactions acting within the Hilbert space of the physical system that implements a logical qubit. The required
order of nonlinearity is often not directly available in the natural interactions of the system. Here, we experimentally demonstrate a route to obtain higher-order nonlinearities by combining more easily available lower-order nonlinear processes, using a generalization of the Raman transitions. In particular, we demonstrate a Raman-assisted transformation of four photons of a high-Q superconducting cavity into two excitations of a superconducting transmon mode and vice versa. The resulting six-quanta process is obtained by cascading two fourth-order nonlinear processes through a virtual state. This process is a key step towards hardware efficient quantum error correction using Schrödinger cat-states.
arxiv pdf

Gated conditional displacement readout of superconducting qubits

  1. S. Touzard,
  2. A. Kou,
  3. N. E. Frattini,
  4. V. V. Sivak,
  5. S. Puri,
  6. A. Grimm,
  7. L. Frunzio,
  8. S. Shankar,
  9. and M.H. Devoret
We have realized a new interaction between superconducting qubits and a readout cavity that results in the displacement of a coherent state in the cavity, conditioned on the state of
the qubit. This conditional state, when it reaches the cavity-following, phase-sensitive amplifier, matches its measured observable, namely the in-phase quadrature. In a setup where several qubits are coupled to the same readout resonator, we show it is possible to measure the state of a target qubit with minimal dephasing of the other qubits. Our results suggest novel directions for faster readout of superconducting qubits and implementations of bosonic quantum error-correcting codes.
arxiv pdf

Optimizing the nonlinearity and dissipation of a SNAIL Parametric Amplifier for dynamic range

  1. N. E. Frattini,
  2. V. V. Sivak,
  3. A. Lingenfelter,
  4. S. Shankar,
  5. and M. H. Devoret
We present a new quantum-limited Josephson-junction-based 3-wave-mixing parametric amplifier, the SNAIL Parametric Amplifier (SPA), which uses an array of SNAILs (Superconducting Nonlinear
Asymmetric Inductive eLements) as the source of tunable nonlinearity. We show how to engineer the nonlinearity over multiple orders of magnitude by varying the physical design of the device. As a function of design parameters, we systematically explore two important amplifier nonidealities that limit dynamic range: the phenomena of gain compression and intermodulation distortion, whose minimization are crucial for high-fidelity multi-qubit readout. Through a comparison with first-principles theory across multiple devices, we demonstrate how to optimize both the nonlinearity and the input-output port coupling of these SNAIL-based parametric amplifiers to achieve higher saturation power, without sacrificing any other desirable characteristics. The method elaborated in our work can be extended to improve all forms of parametrically induced mixing that can be employed for quantum information applications.
arxiv pdf

Driving forbidden transitions in the fluxonium artificial atom

  1. U. Vool,
  2. A. Kou,
  3. W. C. Smith,
  4. N. E. Frattini,
  5. K. Serniak,
  6. P. Reinhold,
  7. I. M. Pop,
  8. S. Shankar,
  9. L. Frunzio,
  10. S. M. Girvin,
  11. and M. H. Devoret
Atomic systems display a rich variety of quantum dynamics due to the different possible symmetries obeyed by the atoms. These symmetries result in selection rules that have been essential
for the quantum control of atomic systems. Superconducting artificial atoms are mainly governed by parity symmetry. Its corresponding selection rule limits the types of quantum systems that can be built using electromagnetic circuits at their optimal coherence operation points („sweet spots“). Here, we use third-order nonlinear coupling between the artificial atom and its readout resonator to drive transitions forbidden by the parity selection rule for linear coupling to microwave radiation. A Lambda-type system emerges from these newly accessible transitions, implemented here in the fluxonium artificial atom coupled to its „antenna“ resonator. We demonstrate coherent manipulation of the fluxonium artificial atom at its sweet spot by stimulated Raman transitions. This type of transition enables the creation of new quantum operations, such as the control and readout of physically protected artificial atoms.
arxiv pdf

3-Wave Mixing Josephson Dipole Element

  1. N. E. Frattini,
  2. U. Vool,
  3. S. Shankar,
  4. A. Narla,
  5. K. M. Sliwa,
  6. and M. H. Devoret
Parametric conversion and amplification based on three-wave mixing are powerful primitives for efficient quantum operations. For superconducting qubits, such operations can be realized
with a quadrupole Josephson junction element, the Josephson Ring Modulator (JRM), which behaves as a loss-less three-wave mixer. However, combining multiple quadrupole elements is a difficult task so it would be advantageous to have a pure three-wave dipole element that could be tessellated for increased power handling and/or information throughput. Here, we present a novel dipole circuit element with third-order nonlinearity, which implements three-wave mixing while minimizing harmful Kerr terms present in the JRM. Experimental results for a non-degenerate amplifier based on the proposed pure third-order nonlinearity are reported.
arxiv pdf