4,409 research outputs found
Geometry-induced memory effects in isolated quantum systems: Observations and applications
Memory effects can lead to history-dependent behavior of a system, and they
are ubiquitous in our daily life and have broad applications. Here we explore
possibilities of generating memory effects in simple isolated quantum systems.
By utilizing geometrical effects from a class of lattices supporting flat-bands
consisting of localized states, memory effects could be observed in ultracold
atoms in optical lattices. As the optical lattice continuously transforms from
a triangular lattice into a kagome lattice with a flat band, history-dependent
density distributions manifest quantum memory effects even in noninteracting
systems, including fermionic as well as bosonic systems in the proper ranges of
temperatures. Rapid growth in ultracold technology predicts a bright future for
quantum memory-effect systems, and here two prototypical applications of
geometry-induced quantum memory effects are proposed: An accelerometer
recording the mechanical change rate in a coupled system and a rate-controlled
memvalve where the rate of ramping the lattice potential acts as a control of
the remnant density in the lattice.Comment: 13 pages, 11 figures, update figures and references. We provided one
more application - quantum memory effects atomic memory (QMEAM
MIMO Transceivers With Decision Feedback and Bit Loading: Theory and Optimization
This paper considers MIMO transceivers with linear precoders and decision feedback equalizers (DFEs), with bit allocation at the transmitter. Zero-forcing (ZF) is assumed. Considered first is the minimization of transmitted power, for a given total bit rate and a specified set of error probabilities for the symbol streams. The precoder and DFE matrices are optimized jointly with bit allocation. It is shown that the generalized triangular decomposition (GTD) introduced by Jiang, Li, and Hager offers an optimal family of solutions. The optimal linear transceiver (which has a linear equalizer rather than a DFE) with optimal bit allocation is a member of this family. This shows formally that, under optimal bit allocation, linear and DFE transceivers achieve the same minimum power. The DFE transceiver using the geometric mean decomposition (GMD) is another member of this optimal family, and is such that optimal bit allocation yields identical bits for all symbol streams—no bit allocation is necessary—when the specified error probabilities are identical for all streams. The QR-based system used in VBLAST is yet another member of the optimal family and is particularly well-suited when limited feedback is allowed from receiver to transmitter. Two other optimization problems are then considered: a) minimization of power for specified set of bit rates and error probabilities (the QoS problem), and b) maximization of bit rate for fixed set of error probabilities and power. It is shown in both cases that the GTD yields an optimal family of solutions
GTD-based transceivers for decision feedback and bit loading
We consider new optimization problems for transceivers with DFE receivers and linear precoders, which also use bit loading at the transmitter. First, we consider the MIMO QoS (quality of service) problem, which is to minimize the total transmitted power when the bit rate and probability of error of each data stream are specified. The developments of this paper are based on the generalized triangular decomposition (GTD) recently introduced by Jiang, Li, and Hager. It is shown that under some multiplicative majorization conditions there exists a custom GTD-based transceiver which achieves the minimal power. The problem of maximizing the bit rate subject to the total power constraint and given error probability is also considered in this paper. It is shown that the GTD-based systems also give the optimal solutions to the bit rate maximization problem
- …