Measuring a transmon qubit in circuit QED: Dressed squeezed states

Khezri, Mostafa; Mlinar, Eric; Dressel, Justin; Korotkov, Alexander N.

doi:10.1103/physreva.94.012347

Cited by 32 publications

(38 citation statements)

References 60 publications

(151 reference statements)

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“…where W I,Q denote independent Wiener processes, obeying the conventional rules, E [W (t)] = 0 and Var [W (t)] = t 2 . Equation (54) shows that the distribution of the stochastic variable s is a Gaussian blob in the IQ plane centered at s B,G ≡ E [s B,G ] = √ ηγT int α B,G with width determined by the variance σ 2 B,G ≡ Var [s B,G ] = 1 2 T int . We can thus define the SNR of the experiment by comparing the distance between the two pointer distributions to their width,…”

Section: Indirect Monitoring Methods With Superconducting Circuitsmentioning

confidence: 99%

To catch and reverse a quantum jump mid-flight

Minev

Mundhada

Shankar

et al. 2019

Nature

307

264

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Quantum physics was invented to account for two fundamental features of measurement resultstheir discreetness and randomness. Emblematic of these features is Bohr's idea of quantum jumps between two discrete energy levels of an atom 1 . Experimentally, quantum jumps were first observed in an atomic ion driven by a weak deterministic force while under strong continuous energy measurement 2-4 . The times at which the discontinuous jump transitions occur are reputed to be fundamentally unpredictable. Can there be, despite the indeterminism of quantum physics, a possibility to know if a quantum jump is about to occur or not? Here, we answer this question affirmatively by experimentally demonstrating that the jump from the ground to an excited state of a superconducting artificial three-level atom can be tracked as it follows a predictable "flight," by monitoring the population of an auxiliary energy level coupled to the ground state. The experimental results demonstrate that the jump evolution when completed is continuous, coherent, and deterministic. Furthermore, exploiting these features and using real-time monitoring and feedback, we catch and reverse a quantum jump mid-flight, thus deterministically preventing its completion. Our results, which agree with theoretical predictions essentially without adjustable parameters, support the modern quantum trajectory theory 5-9 and provide new ground for the exploration of real-time intervention techniques in the control of quantum systems, such as early detection of error syndromes.Bohr conceived of quantum jumps 1 in 1913, and while Einstein elevated their hypothesis to the level of a quantitative rule with his AB coefficient theory 10,11 , Schrödinger strongly objected to their existence 12 . The nature and existence of quantum jumps remained a subject of controversy for seven decades until they were directly observed in a single system 2-4 . Since then, quantum jumps have been observed in a variety of atomic [13][14][15][16] and solid-state 17-21 systems. Recently, quantum jumps have been recognized as an essential phenomenon in quantum feedback control 22,23 , and in particular, for detecting and correcting decoherence-induced errors in quantum information systems 24,25 .

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Section: Indirect Monitoring Methods With Superconducting Circuitsmentioning

confidence: 99%

To catch and reverse a quantum jump mid-flight

Minev

Mundhada

Shankar

et al. 2019

Nature

307

264

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“…It is important to note that the Jaynes-Cummings and dispersive Hamiltonians are connected by a unitary transformation that 'mixes' qubit and cavity observables, and as such the steady-states in the two frames are strictly speaking not directly comparable. However, based on previous work [42,43] the scale of the lowest order effect of this mixing is set by c J , and for our parameter choice (c = J 1 200) this will have only a small effect on a direct comparison of the steady-states. Additionally, as we are primarily interested in the effect the Jaynes-Cummings dynamics has on the cavity state, we treat the even and odd mode decay as independent, and do not model the correlated decay discussed in section 7.…”

Section: C2 Measurement Signalmentioning

confidence: 99%

Enhanced qubit readout using locally generated squeezing and inbuilt Purcell-decay suppression

Govia

Clerk

2017

New J. Phys.

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We introduce and analyze a dispersive qubit readout scheme where two-mode squeezing is generated directly in the measurement cavities. The resulting suppression of noise enables fast, high-fidelity readout of naturally weakly coupled qubits, and the possibility to protect strongly coupled qubits from decoherence by weakening their coupling. Unlike other approaches exploiting squeezing, our setup avoids the difficult task of transporting and injecting with high fidelity an externally generated squeezed state. Our setup is also surprisingly robust against unwanted non-QND backaction effects, as interference naturally suppresses Purcell decay: the system acts as its own Purcell filter. Our setup is compatible with the experimental state-of-the-art in circuit QED systems, but the basic idea could also be realized in other systems.

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“…In addition, there is great interest in using superconducting circuits to realise novel phases [15,16] and quantum phase transitions [17] in driven dissipative lattices, while it is also hoped that a quantum simulator can be constructed from such an array [18]. Efforts to improve the technology further have led to increased use of nonclassical states, for example for improving qubit read out [19,20]. The field of quantum optomechanics [21,22] is concerned with the same fundamental models as circuit QED, albeit in different parameter ranges and can therefore also benefit from the methods discussed here.…”

Section: Introductionmentioning

confidence: 99%

Applications of the Fokker-Planck equation in circuit quantum electrodynamics

Elliott

Ginossar

2016

Phys. Rev. A

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We study exact solutions of the steady state behaviour of several non-linear open quantum systems which can be applied to the field of circuit quantum electrodynamics. Using Fokker-Planck equations in the generalised P -representation we investigate the analytical solutions of two fundamental models. First, we solve for the steady-state response of a linear cavity that is coupled to an approximate transmon qubit and use this solution to study both the weak and strong driving regimes, using analytical expressions for the moments of both cavity and transmon fields, along with the Husimi Q-function for the transmon. Second, we revisit exact solutions of quantum Duffing oscillator which is driven both coherently and parametrically while also experiencing decoherence by the loss of single and pairs of photons. We use this solution to discuss both stabilisation of Schrödinger cat states and the generation of squeezed states in parametric amplifiers, in addition to studying the Q-functions of the different phases of the quantum system. The field of superconducting circuits, with its strong nonlinearities and couplings, has provided access to new parameter regimes in which returning to these exact quantum optics methods can provide valuable insights.

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Measuring a transmon qubit in circuit QED: Dressed squeezed states

Cited by 32 publications

References 60 publications

To catch and reverse a quantum jump mid-flight

To catch and reverse a quantum jump mid-flight

Enhanced qubit readout using locally generated squeezing and inbuilt Purcell-decay suppression

Applications of the Fokker-Planck equation in circuit quantum electrodynamics

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