Limits...
Suppressing qubit dephasing using real-time Hamiltonian estimation.

Shulman MD, Harvey SP, Nichol JM, Bartlett SD, Doherty AC, Umansky V, Yacoby A - Nat Commun (2014)

Bottom Line: Strategies such as environmental and materials engineering, quantum error correction and dynamical decoupling can mitigate decoherence, but generally increase experimental complexity.Here we improve coherence in a qubit using real-time Hamiltonian parameter estimation.Because the technique demonstrated here is compatible with arbitrary qubit operations, it is a natural complement to quantum error correction and can be used to improve the performance of a wide variety of qubits in both meteorological and quantum information processing applications.

View Article: PubMed Central - PubMed

Affiliation: Department of Physics, Harvard University, Cambridge, Massachusetts 02138, USA.

ABSTRACT
Unwanted interaction between a quantum system and its fluctuating environment leads to decoherence and is the primary obstacle to establishing a scalable quantum information processing architecture. Strategies such as environmental and materials engineering, quantum error correction and dynamical decoupling can mitigate decoherence, but generally increase experimental complexity. Here we improve coherence in a qubit using real-time Hamiltonian parameter estimation. Using a rapidly converging Bayesian approach, we precisely measure the splitting in a singlet-triplet spin qubit faster than the surrounding nuclear bath fluctuates. We continuously adjust qubit control parameters based on this information, thereby improving the inhomogenously broadened coherence time (T2*) from tens of nanoseconds to >2 μs. Because the technique demonstrated here is compatible with arbitrary qubit operations, it is a natural complement to quantum error correction and can be used to improve the performance of a wide variety of qubits in both meteorological and quantum information processing applications.

No MeSH data available.


Related in: MedlinePlus

Adaptive control.(a) For these measurements we first perform our standard nuclear feedback, then quickly estimate ΔBz and update the qubit control, then operate the qubit at the correct driving frequency. (b) Using adaptive control, we perform a Ramsey experiment (deliberately detuned to see oscillations) and obtain coherence times of . (c) Histograms of measured Ramsey detunings with (green) and without (blue) adaptive control. For clarity, these data were taken with a different mean detuning than those in b. (d) Raw data for 1,024 consecutive Ramsey experiments with adaptive control lasting 250 s in total. A value of 1 corresponds to /T0› and 0 corresponds to /S›. Stabilized oscillations are clearly visible in the data, demonstrating the effect of adaptive control.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4214408&req=5

f3: Adaptive control.(a) For these measurements we first perform our standard nuclear feedback, then quickly estimate ΔBz and update the qubit control, then operate the qubit at the correct driving frequency. (b) Using adaptive control, we perform a Ramsey experiment (deliberately detuned to see oscillations) and obtain coherence times of . (c) Histograms of measured Ramsey detunings with (green) and without (blue) adaptive control. For clarity, these data were taken with a different mean detuning than those in b. (d) Raw data for 1,024 consecutive Ramsey experiments with adaptive control lasting 250 s in total. A value of 1 corresponds to /T0› and 0 corresponds to /S›. Stabilized oscillations are clearly visible in the data, demonstrating the effect of adaptive control.

Mentions: To take advantage of the slow nuclear dynamics, we introduce a method that measures the fluctuations and manipulates the qubit on the basis of precise knowledge but not precise control of the environment. We operate the qubit in the rotating frame of ΔBz, where qubit rotations are driven by modulating J at the frequency (refs 15, 16). This is in contrast to traditional modes of operation of the S−T0 qubit, which rely on DC voltage pulses. To measure Rabi oscillations, the qubit is adiabatically prepared in the ground state of ΔBz (/ψ›=/↑↓›), and an oscillating J is switched on (Fig. 2e), causing the qubit to precess around J in the rotating frame. In addition, we perform a Ramsey experiment (Fig. 2c) to determine , and as expected, we observe the same decay (Fig. 2d) as Fig. 2b. More precisely, the data in Fig. 2d represent the average of 1,024 experimental repetitions of the same qubit operation sequence immediately following nuclear feedback. The feedback cycle resets ΔBz to its mean value (60 MHz) with residual fluctuations of between experimental repetitions. However, within a given experimental repetition, ΔBz is approximately constant. Therefore we present an adaptive control scheme where, following nuclear feedback, we quickly estimate ΔBz and tune to prolong qubit coherence (Fig. 3a).


Suppressing qubit dephasing using real-time Hamiltonian estimation.

Shulman MD, Harvey SP, Nichol JM, Bartlett SD, Doherty AC, Umansky V, Yacoby A - Nat Commun (2014)

Adaptive control.(a) For these measurements we first perform our standard nuclear feedback, then quickly estimate ΔBz and update the qubit control, then operate the qubit at the correct driving frequency. (b) Using adaptive control, we perform a Ramsey experiment (deliberately detuned to see oscillations) and obtain coherence times of . (c) Histograms of measured Ramsey detunings with (green) and without (blue) adaptive control. For clarity, these data were taken with a different mean detuning than those in b. (d) Raw data for 1,024 consecutive Ramsey experiments with adaptive control lasting 250 s in total. A value of 1 corresponds to /T0› and 0 corresponds to /S›. Stabilized oscillations are clearly visible in the data, demonstrating the effect of adaptive control.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4214408&req=5

f3: Adaptive control.(a) For these measurements we first perform our standard nuclear feedback, then quickly estimate ΔBz and update the qubit control, then operate the qubit at the correct driving frequency. (b) Using adaptive control, we perform a Ramsey experiment (deliberately detuned to see oscillations) and obtain coherence times of . (c) Histograms of measured Ramsey detunings with (green) and without (blue) adaptive control. For clarity, these data were taken with a different mean detuning than those in b. (d) Raw data for 1,024 consecutive Ramsey experiments with adaptive control lasting 250 s in total. A value of 1 corresponds to /T0› and 0 corresponds to /S›. Stabilized oscillations are clearly visible in the data, demonstrating the effect of adaptive control.
Mentions: To take advantage of the slow nuclear dynamics, we introduce a method that measures the fluctuations and manipulates the qubit on the basis of precise knowledge but not precise control of the environment. We operate the qubit in the rotating frame of ΔBz, where qubit rotations are driven by modulating J at the frequency (refs 15, 16). This is in contrast to traditional modes of operation of the S−T0 qubit, which rely on DC voltage pulses. To measure Rabi oscillations, the qubit is adiabatically prepared in the ground state of ΔBz (/ψ›=/↑↓›), and an oscillating J is switched on (Fig. 2e), causing the qubit to precess around J in the rotating frame. In addition, we perform a Ramsey experiment (Fig. 2c) to determine , and as expected, we observe the same decay (Fig. 2d) as Fig. 2b. More precisely, the data in Fig. 2d represent the average of 1,024 experimental repetitions of the same qubit operation sequence immediately following nuclear feedback. The feedback cycle resets ΔBz to its mean value (60 MHz) with residual fluctuations of between experimental repetitions. However, within a given experimental repetition, ΔBz is approximately constant. Therefore we present an adaptive control scheme where, following nuclear feedback, we quickly estimate ΔBz and tune to prolong qubit coherence (Fig. 3a).

Bottom Line: Strategies such as environmental and materials engineering, quantum error correction and dynamical decoupling can mitigate decoherence, but generally increase experimental complexity.Here we improve coherence in a qubit using real-time Hamiltonian parameter estimation.Because the technique demonstrated here is compatible with arbitrary qubit operations, it is a natural complement to quantum error correction and can be used to improve the performance of a wide variety of qubits in both meteorological and quantum information processing applications.

View Article: PubMed Central - PubMed

Affiliation: Department of Physics, Harvard University, Cambridge, Massachusetts 02138, USA.

ABSTRACT
Unwanted interaction between a quantum system and its fluctuating environment leads to decoherence and is the primary obstacle to establishing a scalable quantum information processing architecture. Strategies such as environmental and materials engineering, quantum error correction and dynamical decoupling can mitigate decoherence, but generally increase experimental complexity. Here we improve coherence in a qubit using real-time Hamiltonian parameter estimation. Using a rapidly converging Bayesian approach, we precisely measure the splitting in a singlet-triplet spin qubit faster than the surrounding nuclear bath fluctuates. We continuously adjust qubit control parameters based on this information, thereby improving the inhomogenously broadened coherence time (T2*) from tens of nanoseconds to >2 μs. Because the technique demonstrated here is compatible with arbitrary qubit operations, it is a natural complement to quantum error correction and can be used to improve the performance of a wide variety of qubits in both meteorological and quantum information processing applications.

No MeSH data available.


Related in: MedlinePlus